diff options
| -rw-r--r-- | Documentation/hwlat_detector.txt | 64 | ||||
| -rw-r--r-- | MAINTAINERS | 9 | ||||
| -rw-r--r-- | drivers/misc/Kconfig | 29 | ||||
| -rw-r--r-- | drivers/misc/Makefile | 1 | ||||
| -rw-r--r-- | drivers/misc/hwlat_detector.c | 1212 |
5 files changed, 1315 insertions, 0 deletions
diff --git a/Documentation/hwlat_detector.txt b/Documentation/hwlat_detector.txt new file mode 100644 index 000000000000..cb61516483d3 --- /dev/null +++ b/Documentation/hwlat_detector.txt @@ -0,0 +1,64 @@ +Introduction: +------------- + +The module hwlat_detector is a special purpose kernel module that is used to +detect large system latencies induced by the behavior of certain underlying +hardware or firmware, independent of Linux itself. The code was developed +originally to detect SMIs (System Management Interrupts) on x86 systems, +however there is nothing x86 specific about this patchset. It was +originally written for use by the "RT" patch since the Real Time +kernel is highly latency sensitive. + +SMIs are usually not serviced by the Linux kernel, which typically does not +even know that they are occuring. SMIs are instead are set up by BIOS code +and are serviced by BIOS code, usually for "critical" events such as +management of thermal sensors and fans. Sometimes though, SMIs are used for +other tasks and those tasks can spend an inordinate amount of time in the +handler (sometimes measured in milliseconds). Obviously this is a problem if +you are trying to keep event service latencies down in the microsecond range. + +The hardware latency detector works by hogging all of the cpus for configurable +amounts of time (by calling stop_machine()), polling the CPU Time Stamp Counter +for some period, then looking for gaps in the TSC data. Any gap indicates a +time when the polling was interrupted and since the machine is stopped and +interrupts turned off the only thing that could do that would be an SMI. + +Note that the SMI detector should *NEVER* be used in a production environment. +It is intended to be run manually to determine if the hardware platform has a +problem with long system firmware service routines. + +Usage: +------ + +Loading the module hwlat_detector passing the parameter "enabled=1" (or by +setting the "enable" entry in "hwlat_detector" debugfs toggled on) is the only +step required to start the hwlat_detector. It is possible to redefine the +threshold in microseconds (us) above which latency spikes will be taken +into account (parameter "threshold="). + +Example: + + # modprobe hwlat_detector enabled=1 threshold=100 + +After the module is loaded, it creates a directory named "hwlat_detector" under +the debugfs mountpoint, "/debug/hwlat_detector" for this text. It is necessary +to have debugfs mounted, which might be on /sys/debug on your system. + +The /debug/hwlat_detector interface contains the following files: + +count - number of latency spikes observed since last reset +enable - a global enable/disable toggle (0/1), resets count +max - maximum hardware latency actually observed (usecs) +sample - a pipe from which to read current raw sample data + in the format <timestamp> <latency observed usecs> + (can be opened O_NONBLOCK for a single sample) +threshold - minimum latency value to be considered (usecs) +width - time period to sample with CPUs held (usecs) + must be less than the total window size (enforced) +window - total period of sampling, width being inside (usecs) + +By default we will set width to 500,000 and window to 1,000,000, meaning that +we will sample every 1,000,000 usecs (1s) for 500,000 usecs (0.5s). If we +observe any latencies that exceed the threshold (initially 100 usecs), +then we write to a global sample ring buffer of 8K samples, which is +consumed by reading from the "sample" (pipe) debugfs file interface. diff --git a/MAINTAINERS b/MAINTAINERS index f986e7dc904b..b2574771c3bc 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3008,6 +3008,15 @@ L: linuxppc-dev@lists.ozlabs.org S: Odd Fixes F: drivers/tty/hvc/ +HARDWARE LATENCY DETECTOR +P: Jon Masters +M: jcm@jonmasters.org +W: http://www.kernel.org/pub/linux/kernel/people/jcm/hwlat_detector/ +S: Supported +L: linux-kernel@vger.kernel.org +F: Documentation/hwlat_detector.txt +F: drivers/misc/hwlat_detector.c + HARDWARE MONITORING M: Jean Delvare <khali@linux-fr.org> M: Guenter Roeck <guenter.roeck@ericsson.com> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig index f3031a4b46d8..1cb530c1bc3c 100644 --- a/drivers/misc/Kconfig +++ b/drivers/misc/Kconfig @@ -140,6 +140,35 @@ config IBM_ASM for information on the specific driver level and support statement for your IBM server. +config HWLAT_DETECTOR + tristate "Testing module to detect hardware-induced latencies" + depends on DEBUG_FS + depends on RING_BUFFER + default m + ---help--- + A simple hardware latency detector. Use this module to detect + large latencies introduced by the behavior of the underlying + system firmware external to Linux. We do this using periodic + use of stop_machine to grab all available CPUs and measure + for unexplainable gaps in the CPU timestamp counter(s). By + default, the module is not enabled until the "enable" file + within the "hwlat_detector" debugfs directory is toggled. + + This module is often used to detect SMI (System Management + Interrupts) on x86 systems, though is not x86 specific. To + this end, we default to using a sample window of 1 second, + during which we will sample for 0.5 seconds. If an SMI or + similar event occurs during that time, it is recorded + into an 8K samples global ring buffer until retreived. + + WARNING: This software should never be enabled (it can be built + but should not be turned on after it is loaded) in a production + environment where high latencies are a concern since the + sampling mechanism actually introduces latencies for + regular tasks while the CPU(s) are being held. + + If unsure, say N + config PHANTOM tristate "Sensable PHANToM (PCI)" depends on PCI diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile index b26495a02554..84c45540db3a 100644 --- a/drivers/misc/Makefile +++ b/drivers/misc/Makefile @@ -48,3 +48,4 @@ obj-y += lis3lv02d/ obj-y += carma/ obj-$(CONFIG_USB_SWITCH_FSA9480) += fsa9480.o obj-$(CONFIG_ALTERA_STAPL) +=altera-stapl/ +obj-$(CONFIG_HWLAT_DETECTOR) += hwlat_detector.o diff --git a/drivers/misc/hwlat_detector.c b/drivers/misc/hwlat_detector.c new file mode 100644 index 000000000000..b7b7c903f88d --- /dev/null +++ b/drivers/misc/hwlat_detector.c @@ -0,0 +1,1212 @@ +/* + * hwlat_detector.c - A simple Hardware Latency detector. + * + * Use this module to detect large system latencies induced by the behavior of + * certain underlying system hardware or firmware, independent of Linux itself. + * The code was developed originally to detect the presence of SMIs on Intel + * and AMD systems, although there is no dependency upon x86 herein. + * + * The classical example usage of this module is in detecting the presence of + * SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a + * somewhat special form of hardware interrupt spawned from earlier CPU debug + * modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge + * LPC (or other device) to generate a special interrupt under certain + * circumstances, for example, upon expiration of a special SMI timer device, + * due to certain external thermal readings, on certain I/O address accesses, + * and other situations. An SMI hits a special CPU pin, triggers a special + * SMI mode (complete with special memory map), and the OS is unaware. + * + * Although certain hardware-inducing latencies are necessary (for example, + * a modern system often requires an SMI handler for correct thermal control + * and remote management) they can wreak havoc upon any OS-level performance + * guarantees toward low-latency, especially when the OS is not even made + * aware of the presence of these interrupts. For this reason, we need a + * somewhat brute force mechanism to detect these interrupts. In this case, + * we do it by hogging all of the CPU(s) for configurable timer intervals, + * sampling the built-in CPU timer, looking for discontiguous readings. + * + * WARNING: This implementation necessarily introduces latencies. Therefore, + * you should NEVER use this module in a production environment + * requiring any kind of low-latency performance guarantee(s). + * + * Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com> + * + * Includes useful feedback from Clark Williams <clark@redhat.com> + * + * This file is licensed under the terms of the GNU General Public + * License version 2. This program is licensed "as is" without any + * warranty of any kind, whether express or implied. + */ + +#include <linux/module.h> +#include <linux/init.h> +#include <linux/ring_buffer.h> +#include <linux/stop_machine.h> +#include <linux/time.h> +#include <linux/hrtimer.h> +#include <linux/kthread.h> +#include <linux/debugfs.h> +#include <linux/seq_file.h> +#include <linux/uaccess.h> +#include <linux/version.h> +#include <linux/delay.h> +#include <linux/slab.h> + +#define BUF_SIZE_DEFAULT 262144UL /* 8K*(sizeof(entry)) */ +#define BUF_FLAGS (RB_FL_OVERWRITE) /* no block on full */ +#define U64STR_SIZE 22 /* 20 digits max */ + +#define VERSION "1.0.0" +#define BANNER "hwlat_detector: " +#define DRVNAME "hwlat_detector" +#define DEFAULT_SAMPLE_WINDOW 1000000 /* 1s */ +#define DEFAULT_SAMPLE_WIDTH 500000 /* 0.5s */ +#define DEFAULT_LAT_THRESHOLD 10 /* 10us */ + +/* Module metadata */ + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Jon Masters <jcm@redhat.com>"); +MODULE_DESCRIPTION("A simple hardware latency detector"); +MODULE_VERSION(VERSION); + +/* Module parameters */ + +static int debug; +static int enabled; +static int threshold; + +module_param(debug, int, 0); /* enable debug */ +module_param(enabled, int, 0); /* enable detector */ +module_param(threshold, int, 0); /* latency threshold */ + +/* Buffering and sampling */ + +static struct ring_buffer *ring_buffer; /* sample buffer */ +static DEFINE_MUTEX(ring_buffer_mutex); /* lock changes */ +static unsigned long buf_size = BUF_SIZE_DEFAULT; +static struct task_struct *kthread; /* sampling thread */ + +/* DebugFS filesystem entries */ + +static struct dentry *debug_dir; /* debugfs directory */ +static struct dentry *debug_max; /* maximum TSC delta */ +static struct dentry *debug_count; /* total detect count */ +static struct dentry *debug_sample_width; /* sample width us */ +static struct dentry *debug_sample_window; /* sample window us */ +static struct dentry *debug_sample; /* raw samples us */ +static struct dentry *debug_threshold; /* threshold us */ +static struct dentry *debug_enable; /* enable/disable */ + +/* Individual samples and global state */ + +struct sample; /* latency sample */ +struct data; /* Global state */ + +/* Sampling functions */ +static int __buffer_add_sample(struct sample *sample); +static struct sample *buffer_get_sample(struct sample *sample); +static int get_sample(void *unused); + +/* Threading and state */ +static int kthread_fn(void *unused); +static int start_kthread(void); +static int stop_kthread(void); +static void __reset_stats(void); +static int init_stats(void); + +/* Debugfs interface */ +static ssize_t simple_data_read(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos, const u64 *entry); +static ssize_t simple_data_write(struct file *filp, const char __user *ubuf, + size_t cnt, loff_t *ppos, u64 *entry); +static int debug_sample_fopen(struct inode *inode, struct file *filp); +static ssize_t debug_sample_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos); +static int debug_sample_release(struct inode *inode, struct file *filp); +static int debug_enable_fopen(struct inode *inode, struct file *filp); +static ssize_t debug_enable_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos); +static ssize_t debug_enable_fwrite(struct file *file, + const char __user *user_buffer, + size_t user_size, loff_t *offset); + +/* Initialization functions */ +static int init_debugfs(void); +static void free_debugfs(void); +static int detector_init(void); +static void detector_exit(void); + +/* Individual latency samples are stored here when detected and packed into + * the ring_buffer circular buffer, where they are overwritten when + * more than buf_size/sizeof(sample) samples are received. */ +struct sample { + u64 seqnum; /* unique sequence */ + u64 duration; /* ktime delta */ + struct timespec timestamp; /* wall time */ + unsigned long lost; +}; + +/* keep the global state somewhere. Mostly used under stop_machine. */ +static struct data { + + struct mutex lock; /* protect changes */ + + u64 count; /* total since reset */ + u64 max_sample; /* max hardware latency */ + u64 threshold; /* sample threshold level */ + + u64 sample_window; /* total sampling window (on+off) */ + u64 sample_width; /* active sampling portion of window */ + + atomic_t sample_open; /* whether the sample file is open */ + + wait_queue_head_t wq; /* waitqeue for new sample values */ + +} data; + +/** + * __buffer_add_sample - add a new latency sample recording to the ring buffer + * @sample: The new latency sample value + * + * This receives a new latency sample and records it in a global ring buffer. + * No additional locking is used in this case - suited for stop_machine use. + */ +static int __buffer_add_sample(struct sample *sample) +{ + return ring_buffer_write(ring_buffer, + sizeof(struct sample), sample); +} + +/** + * buffer_get_sample - remove a hardware latency sample from the ring buffer + * @sample: Pre-allocated storage for the sample + * + * This retrieves a hardware latency sample from the global circular buffer + */ +static struct sample *buffer_get_sample(struct sample *sample) +{ + struct ring_buffer_event *e = NULL; + struct sample *s = NULL; + unsigned int cpu = 0; + + if (!sample) + return NULL; + + mutex_lock(&ring_buffer_mutex); + for_each_online_cpu(cpu) { + e = ring_buffer_consume(ring_buffer, cpu, NULL, &sample->lost); + if (e) + break; + } + + if (e) { + s = ring_buffer_event_data(e); + memcpy(sample, s, sizeof(struct sample)); + } else + sample = NULL; + mutex_unlock(&ring_buffer_mutex); + + return sample; +} + +/** + * get_sample - sample the CPU TSC and look for likely hardware latencies + * @unused: This is not used but is a part of the stop_machine API + * + * Used to repeatedly capture the CPU TSC (or similar), looking for potential + * hardware-induced latency. Called under stop_machine, with data.lock held. + */ +static int get_sample(void *unused) +{ + ktime_t start, t1, t2; + s64 diff, total = 0; + u64 sample = 0; + int ret = 1; + + start = ktime_get(); /* start timestamp */ + + do { + + t1 = ktime_get(); /* we'll look for a discontinuity */ + t2 = ktime_get(); + + total = ktime_to_us(ktime_sub(t2, start)); /* sample width */ + diff = ktime_to_us(ktime_sub(t2, t1)); /* current diff */ + + /* This shouldn't happen */ + if (diff < 0) { + printk(KERN_ERR BANNER "time running backwards\n"); + goto out; + } + + if (diff > sample) + sample = diff; /* only want highest value */ + + } while (total <= data.sample_width); + + /* If we exceed the threshold value, we have found a hardware latency */ + if (sample > data.threshold) { + struct sample s; + + data.count++; + s.seqnum = data.count; + s.duration = sample; + s.timestamp = CURRENT_TIME; + __buffer_add_sample(&s); + + /* Keep a running maximum ever recorded hardware latency */ + if (sample > data.max_sample) + data.max_sample = sample; + } + + ret = 0; +out: + return ret; +} + +/* + * kthread_fn - The CPU time sampling/hardware latency detection kernel thread + * @unused: A required part of the kthread API. + * + * Used to periodically sample the CPU TSC via a call to get_sample. We + * use stop_machine, whith does (intentionally) introduce latency since we + * need to ensure nothing else might be running (and thus pre-empting). + * Obviously this should never be used in production environments. + * + * stop_machine will schedule us typically only on CPU0 which is fine for + * almost every real-world hardware latency situation - but we might later + * generalize this if we find there are any actualy systems with alternate + * SMI delivery or other non CPU0 hardware latencies. + */ +static int kthread_fn(void *unused) +{ + int err = 0; + u64 interval = 0; + + while (!kthread_should_stop()) { + + mutex_lock(&data.lock); + + err = stop_machine(get_sample, unused, 0); + if (err) { + /* Houston, we have a problem */ + mutex_unlock(&data.lock); + goto err_out; + } + + wake_up(&data.wq); /* wake up reader(s) */ + + interval = data.sample_window - data.sample_width; + do_div(interval, USEC_PER_MSEC); /* modifies interval value */ + + mutex_unlock(&data.lock); + + if (msleep_interruptible(interval)) + goto out; + } + goto out; +err_out: + printk(KERN_ERR BANNER "could not call stop_machine, disabling\n"); + enabled = 0; +out: + return err; + +} + +/** + * start_kthread - Kick off the hardware latency sampling/detector kthread + * + * This starts a kernel thread that will sit and sample the CPU timestamp + * counter (TSC or similar) and look for potential hardware latencies. + */ +static int start_kthread(void) +{ + kthread = kthread_run(kthread_fn, NULL, + DRVNAME); + if (IS_ERR(kthread)) { + printk(KERN_ERR BANNER "could not start sampling thread\n"); + enabled = 0; + return -ENOMEM; + } + + return 0; +} + +/** + * stop_kthread - Inform the hardware latency samping/detector kthread to stop + * + * This kicks the running hardware latency sampling/detector kernel thread and + * tells it to stop sampling now. Use this on unload and at system shutdown. + */ +static int stop_kthread(void) +{ + int ret; + + ret = kthread_stop(kthread); + + return ret; +} + +/** + * __reset_stats - Reset statistics for the hardware latency detector + * + * We use data to store various statistics and global state. We call this + * function in order to reset those when "enable" is toggled on or off, and + * also at initialization. Should be called with data.lock held. + */ +static void __reset_stats(void) +{ + data.count = 0; + data.max_sample = 0; + ring_buffer_reset(ring_buffer); /* flush out old sample entries */ +} + +/** + * init_stats - Setup global state statistics for the hardware latency detector + * + * We use data to store various statistics and global state. We also use + * a global ring buffer (ring_buffer) to keep raw samples of detected hardware + * induced system latencies. This function initializes these structures and + * allocates the global ring buffer also. + */ +static int init_stats(void) +{ + int ret = -ENOMEM; + + mutex_init(&data.lock); + init_waitqueue_head(&data.wq); + atomic_set(&data.sample_open, 0); + + ring_buffer = ring_buffer_alloc(buf_size, BUF_FLAGS); + + if (WARN(!ring_buffer, KERN_ERR BANNER + "failed to allocate ring buffer!\n")) + goto out; + + __reset_stats(); + data.threshold = DEFAULT_LAT_THRESHOLD; /* threshold us */ + data.sample_window = DEFAULT_SAMPLE_WINDOW; /* window us */ + data.sample_width = DEFAULT_SAMPLE_WIDTH; /* width us */ + + ret = 0; + +out: + return ret; + +} + +/* + * simple_data_read - Wrapper read function for global state debugfs entries + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * @entry: The entry to read from + * + * This function provides a generic read implementation for the global state + * "data" structure debugfs filesystem entries. It would be nice to use + * simple_attr_read directly, but we need to make sure that the data.lock + * spinlock is held during the actual read (even though we likely won't ever + * actually race here as the updater runs under a stop_machine context). + */ +static ssize_t simple_data_read(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos, const u64 *entry) +{ + char buf[U64STR_SIZE]; + u64 val = 0; + int len = 0; + + memset(buf, 0, sizeof(buf)); + + if (!entry) + return -EFAULT; + + mutex_lock(&data.lock); + val = *entry; + mutex_unlock(&data.lock); + + len = snprintf(buf, sizeof(buf), "%llu\n", (unsigned long long)val); + + return simple_read_from_buffer(ubuf, cnt, ppos, buf, len); + +} + +/* + * simple_data_write - Wrapper write function for global state debugfs entries + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to write value from + * @cnt: The maximum number of bytes to write + * @ppos: The current "file" position + * @entry: The entry to write to + * + * This function provides a generic write implementation for the global state + * "data" structure debugfs filesystem entries. It would be nice to use + * simple_attr_write directly, but we need to make sure that the data.lock + * spinlock is held during the actual write (even though we likely won't ever + * actually race here as the updater runs under a stop_machine context). + */ +static ssize_t simple_data_write(struct file *filp, const char __user *ubuf, + size_t cnt, loff_t *ppos, u64 *entry) +{ + char buf[U64STR_SIZE]; + int csize = min(cnt, sizeof(buf)); + u64 val = 0; + int err = 0; + + memset(buf, '\0', sizeof(buf)); + if (copy_from_user(buf, ubuf, csize)) + return -EFAULT; + + buf[U64STR_SIZE-1] = '\0'; /* just in case */ + err = strict_strtoull(buf, 10, &val); + if (err) + return -EINVAL; + + mutex_lock(&data.lock); + *entry = val; + mutex_unlock(&data.lock); + + return csize; +} + +/** + * debug_count_fopen - Open function for "count" debugfs entry + * @inode: The in-kernel inode representation of the debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function provides an open implementation for the "count" debugfs + * interface to the hardware latency detector. + */ +static int debug_count_fopen(struct inode *inode, struct file *filp) +{ + return 0; +} + +/** + * debug_count_fread - Read function for "count" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * + * This function provides a read implementation for the "count" debugfs + * interface to the hardware latency detector. Can be used to read the + * number of latency readings exceeding the configured threshold since + * the detector was last reset (e.g. by writing a zero into "count"). + */ +static ssize_t debug_count_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + return simple_data_read(filp, ubuf, cnt, ppos, &data.count); +} + +/** + * debug_count_fwrite - Write function for "count" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The user buffer that contains the value to write + * @cnt: The maximum number of bytes to write to "file" + * @ppos: The current position in the debugfs "file" + * + * This function provides a write implementation for the "count" debugfs + * interface to the hardware latency detector. Can be used to write a + * desired value, especially to zero the total count. + */ +static ssize_t debug_count_fwrite(struct file *filp, + const char __user *ubuf, + size_t cnt, + loff_t *ppos) +{ + return simple_data_write(filp, ubuf, cnt, ppos, &data.count); +} + +/** + * debug_enable_fopen - Dummy open function for "enable" debugfs interface + * @inode: The in-kernel inode representation of the debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function provides an open implementation for the "enable" debugfs + * interface to the hardware latency detector. + */ +static int debug_enable_fopen(struct inode *inode, struct file *filp) +{ + return 0; +} + +/** + * debug_enable_fread - Read function for "enable" debugfs interface + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * + * This function provides a read implementation for the "enable" debugfs + * interface to the hardware latency detector. Can be used to determine + * whether the detector is currently enabled ("0\n" or "1\n" returned). + */ +static ssize_t debug_enable_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + char buf[4]; + + if ((cnt < sizeof(buf)) || (*ppos)) + return 0; + + buf[0] = enabled ? '1' : '0'; + buf[1] = '\n'; + buf[2] = '\0'; + if (copy_to_user(ubuf, buf, strlen(buf))) + return -EFAULT; + return *ppos = strlen(buf); +} + +/** + * debug_enable_fwrite - Write function for "enable" debugfs interface + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The user buffer that contains the value to write + * @cnt: The maximum number of bytes to write to "file" + * @ppos: The current position in the debugfs "file" + * + * This function provides a write implementation for the "enable" debugfs + * interface to the hardware latency detector. Can be used to enable or + * disable the detector, which will have the side-effect of possibly + * also resetting the global stats and kicking off the measuring + * kthread (on an enable) or the converse (upon a disable). + */ +static ssize_t debug_enable_fwrite(struct file *filp, + const char __user *ubuf, + size_t cnt, + loff_t *ppos) +{ + char buf[4]; + int csize = min(cnt, sizeof(buf)); + long val = 0; + int err = 0; + + memset(buf, '\0', sizeof(buf)); + if (copy_from_user(buf, ubuf, csize)) + return -EFAULT; + + buf[sizeof(buf)-1] = '\0'; /* just in case */ + err = strict_strtoul(buf, 10, &val); + if (0 != err) + return -EINVAL; + + if (val) { + if (enabled) + goto unlock; + enabled = 1; + __reset_stats(); + if (start_kthread()) + return -EFAULT; + } else { + if (!enabled) + goto unlock; + enabled = 0; + err = stop_kthread(); + if (err) { + printk(KERN_ERR BANNER "cannot stop kthread\n"); + return -EFAULT; + } + wake_up(&data.wq); /* reader(s) should return */ + } +unlock: + return csize; +} + +/** + * debug_max_fopen - Open function for "max" debugfs entry + * @inode: The in-kernel inode representation of the debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function provides an open implementation for the "max" debugfs + * interface to the hardware latency detector. + */ +static int debug_max_fopen(struct inode *inode, struct file *filp) +{ + return 0; +} + +/** + * debug_max_fread - Read function for "max" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * + * This function provides a read implementation for the "max" debugfs + * interface to the hardware latency detector. Can be used to determine + * the maximum latency value observed since it was last reset. + */ +static ssize_t debug_max_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + return simple_data_read(filp, ubuf, cnt, ppos, &data.max_sample); +} + +/** + * debug_max_fwrite - Write function for "max" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The user buffer that contains the value to write + * @cnt: The maximum number of bytes to write to "file" + * @ppos: The current position in the debugfs "file" + * + * This function provides a write implementation for the "max" debugfs + * interface to the hardware latency detector. Can be used to reset the + * maximum or set it to some other desired value - if, then, subsequent + * measurements exceed this value, the maximum will be updated. + */ +static ssize_t debug_max_fwrite(struct file *filp, + const char __user *ubuf, + size_t cnt, + loff_t *ppos) +{ + return simple_data_write(filp, ubuf, cnt, ppos, &data.max_sample); +} + + +/** + * debug_sample_fopen - An open function for "sample" debugfs interface + * @inode: The in-kernel inode representation of this debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function handles opening the "sample" file within the hardware + * latency detector debugfs directory interface. This file is used to read + * raw samples from the global ring_buffer and allows the user to see a + * running latency history. Can be opened blocking or non-blocking, + * affecting whether it behaves as a buffer read pipe, or does not. + * Implements simple locking to prevent multiple simultaneous use. + */ +static int debug_sample_fopen(struct inode *inode, struct file *filp) +{ + if (!atomic_add_unless(&data.sample_open, 1, 1)) + return -EBUSY; + else + return 0; +} + +/** + * debug_sample_fread - A read function for "sample" debugfs interface + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The user buffer that will contain the samples read + * @cnt: The maximum bytes to read from the debugfs "file" + * @ppos: The current position in the debugfs "file" + * + * This function handles reading from the "sample" file within the hardware + * latency detector debugfs directory interface. This file is used to read + * raw samples from the global ring_buffer and allows the user to see a + * running latency history. By default this will block pending a new + * value written into the sample buffer, unless there are already a + * number of value(s) waiting in the buffer, or the sample file was + * previously opened in a non-blocking mode of operation. + */ +static ssize_t debug_sample_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + int len = 0; + char buf[64]; + struct sample *sample = NULL; + + if (!enabled) + return 0; + + sample = kzalloc(sizeof(struct sample), GFP_KERNEL); + if (!sample) + return -ENOMEM; + + while (!buffer_get_sample(sample)) { + + DEFINE_WAIT(wait); + + if (filp->f_flags & O_NONBLOCK) { + len = -EAGAIN; + goto out; + } + + prepare_to_wait(&data.wq, &wait, TASK_INTERRUPTIBLE); + schedule(); + finish_wait(&data.wq, &wait); + + if (signal_pending(current)) { + len = -EINTR; + goto out; + } + + if (!enabled) { /* enable was toggled */ + len = 0; + goto out; + } + } + + len = snprintf(buf, sizeof(buf), "%010lu.%010lu\t%llu\n", + sample->timestamp.tv_sec, + sample->timestamp.tv_nsec, + sample->duration); + + + /* handling partial reads is more trouble than it's worth */ + if (len > cnt) + goto out; + + if (copy_to_user(ubuf, buf, len)) + len = -EFAULT; + +out: + kfree(sample); + return len; +} + +/** + * debug_sample_release - Release function for "sample" debugfs interface + * @inode: The in-kernel inode represenation of the debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function completes the close of the debugfs interface "sample" file. + * Frees the sample_open "lock" so that other users may open the interface. + */ +static int debug_sample_release(struct inode *inode, struct file *filp) +{ + atomic_dec(&data.sample_open); + + return 0; +} + +/** + * debug_threshold_fopen - Open function for "threshold" debugfs entry + * @inode: The in-kernel inode representation of the debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function provides an open implementation for the "threshold" debugfs + * interface to the hardware latency detector. + */ +static int debug_threshold_fopen(struct inode *inode, struct file *filp) +{ + return 0; +} + +/** + * debug_threshold_fread - Read function for "threshold" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * + * This function provides a read implementation for the "threshold" debugfs + * interface to the hardware latency detector. It can be used to determine + * the current threshold level at which a latency will be recorded in the + * global ring buffer, typically on the order of 10us. + */ +static ssize_t debug_threshold_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + return simple_data_read(filp, ubuf, cnt, ppos, &data.threshold); +} + +/** + * debug_threshold_fwrite - Write function for "threshold" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The user buffer that contains the value to write + * @cnt: The maximum number of bytes to write to "file" + * @ppos: The current position in the debugfs "file" + * + * This function provides a write implementation for the "threshold" debugfs + * interface to the hardware latency detector. It can be used to configure + * the threshold level at which any subsequently detected latencies will + * be recorded into the global ring buffer. + */ +static ssize_t debug_threshold_fwrite(struct file *filp, + const char __user *ubuf, + size_t cnt, + loff_t *ppos) +{ + int ret; + + ret = simple_data_write(filp, ubuf, cnt, ppos, &data.threshold); + + if (enabled) + wake_up_process(kthread); + + return ret; +} + +/** + * debug_width_fopen - Open function for "width" debugfs entry + * @inode: The in-kernel inode representation of the debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function provides an open implementation for the "width" debugfs + * interface to the hardware latency detector. + */ +static int debug_width_fopen(struct inode *inode, struct file *filp) +{ + return 0; +} + +/** + * debug_width_fread - Read function for "width" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * + * This function provides a read implementation for the "width" debugfs + * interface to the hardware latency detector. It can be used to determine + * for how many us of the total window us we will actively sample for any + * hardware-induced latecy periods. Obviously, it is not possible to + * sample constantly and have the system respond to a sample reader, or, + * worse, without having the system appear to have gone out to lunch. + */ +static ssize_t debug_width_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + return simple_data_read(filp, ubuf, cnt, ppos, &data.sample_width); +} + +/** + * debug_width_fwrite - Write function for "width" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The user buffer that contains the value to write + * @cnt: The maximum number of bytes to write to "file" + * @ppos: The current position in the debugfs "file" + * + * This function provides a write implementation for the "width" debugfs + * interface to the hardware latency detector. It can be used to configure + * for how many us of the total window us we will actively sample for any + * hardware-induced latency periods. Obviously, it is not possible to + * sample constantly and have the system respond to a sample reader, or, + * worse, without having the system appear to have gone out to lunch. It + * is enforced that width is less that the total window size. + */ +static ssize_t debug_width_fwrite(struct file *filp, + const char __user *ubuf, + size_t cnt, + loff_t *ppos) +{ + char buf[U64STR_SIZE]; + int csize = min(cnt, sizeof(buf)); + u64 val = 0; + int err = 0; + + memset(buf, '\0', sizeof(buf)); + if (copy_from_user(buf, ubuf, csize)) + return -EFAULT; + + buf[U64STR_SIZE-1] = '\0'; /* just in case */ + err = strict_strtoull(buf, 10, &val); + if (0 != err) + return -EINVAL; + + mutex_lock(&data.lock); + if (val < data.sample_window) + data.sample_width = val; + else { + mutex_unlock(&data.lock); + return -EINVAL; + } + mutex_unlock(&data.lock); + + if (enabled) + wake_up_process(kthread); + + return csize; +} + +/** + * debug_window_fopen - Open function for "window" debugfs entry + * @inode: The in-kernel inode representation of the debugfs "file" + * @filp: The active open file structure for the debugfs "file" + * + * This function provides an open implementation for the "window" debugfs + * interface to the hardware latency detector. The window is the total time + * in us that will be considered one sample period. Conceptually, windows + * occur back-to-back and contain a sample width period during which + * actual sampling occurs. + */ +static int debug_window_fopen(struct inode *inode, struct file *filp) +{ + return 0; +} + +/** + * debug_window_fread - Read function for "window" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * + * This function provides a read implementation for the "window" debugfs + * interface to the hardware latency detector. The window is the total time + * in us that will be considered one sample period. Conceptually, windows + * occur back-to-back and contain a sample width period during which + * actual sampling occurs. Can be used to read the total window size. + */ +static ssize_t debug_window_fread(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + return simple_data_read(filp, ubuf, cnt, ppos, &data.sample_window); +} + +/** + * debug_window_fwrite - Write function for "window" debugfs entry + * @filp: The active open file structure for the debugfs "file" + * @ubuf: The user buffer that contains the value to write + * @cnt: The maximum number of bytes to write to "file" + * @ppos: The current position in the debugfs "file" + * + * This function provides a write implementation for the "window" debufds + * interface to the hardware latency detetector. The window is the total time + * in us that will be considered one sample period. Conceptually, windows + * occur back-to-back and contain a sample width period during which + * actual sampling occurs. Can be used to write a new total window size. It + * is enfoced that any value written must be greater than the sample width + * size, or an error results. + */ +static ssize_t debug_window_fwrite(struct file *filp, + const char __user *ubuf, + size_t cnt, + loff_t *ppos) +{ + char buf[U64STR_SIZE]; + int csize = min(cnt, sizeof(buf)); + u64 val = 0; + int err = 0; + + memset(buf, '\0', sizeof(buf)); + if (copy_from_user(buf, ubuf, csize)) + return -EFAULT; + + buf[U64STR_SIZE-1] = '\0'; /* just in case */ + err = strict_strtoull(buf, 10, &val); + if (0 != err) + return -EINVAL; + + mutex_lock(&data.lock); + if (data.sample_width < val) + data.sample_window = val; + else { + mutex_unlock(&data.lock); + return -EINVAL; + } + mutex_unlock(&data.lock); + + return csize; +} + +/* + * Function pointers for the "count" debugfs file operations + */ +static const struct file_operations count_fops = { + .open = debug_count_fopen, + .read = debug_count_fread, + .write = debug_count_fwrite, + .owner = THIS_MODULE, +}; + +/* + * Function pointers for the "enable" debugfs file operations + */ +static const struct file_operations enable_fops = { + .open = debug_enable_fopen, + .read = debug_enable_fread, + .write = debug_enable_fwrite, + .owner = THIS_MODULE, +}; + +/* + * Function pointers for the "max" debugfs file operations + */ +static const struct file_operations max_fops = { + .open = debug_max_fopen, + .read = debug_max_fread, + .write = debug_max_fwrite, + .owner = THIS_MODULE, +}; + +/* + * Function pointers for the "sample" debugfs file operations + */ +static const struct file_operations sample_fops = { + .open = debug_sample_fopen, + .read = debug_sample_fread, + .release = debug_sample_release, + .owner = THIS_MODULE, +}; + +/* + * Function pointers for the "threshold" debugfs file operations + */ +static const struct file_operations threshold_fops = { + .open = debug_threshold_fopen, + .read = debug_threshold_fread, + .write = debug_threshold_fwrite, + .owner = THIS_MODULE, +}; + +/* + * Function pointers for the "width" debugfs file operations + */ +static const struct file_operations width_fops = { + .open = debug_width_fopen, + .read = debug_width_fread, + .write = debug_width_fwrite, + .owner = THIS_MODULE, +}; + +/* + * Function pointers for the "window" debugfs file operations + */ +static const struct file_operations window_fops = { + .open = debug_window_fopen, + .read = debug_window_fread, + .write = debug_window_fwrite, + .owner = THIS_MODULE, +}; + +/** + * init_debugfs - A function to initialize the debugfs interface files + * + * This function creates entries in debugfs for "hwlat_detector", including + * files to read values from the detector, current samples, and the + * maximum sample that has been captured since the hardware latency + * dectector was started. + */ +static int init_debugfs(void) +{ + int ret = -ENOMEM; + + debug_dir = debugfs_create_dir(DRVNAME, NULL); + if (!debug_dir) + goto err_debug_dir; + + debug_sample = debugfs_create_file("sample", 0444, + debug_dir, NULL, + &sample_fops); + if (!debug_sample) + goto err_sample; + + debug_count = debugfs_create_file("count", 0444, + debug_dir, NULL, + &count_fops); + if (!debug_count) + goto err_count; + + debug_max = debugfs_create_file("max", 0444, + debug_dir, NULL, + &max_fops); + if (!debug_max) + goto err_max; + + debug_sample_window = debugfs_create_file("window", 0644, + debug_dir, NULL, + &window_fops); + if (!debug_sample_window) + goto err_window; + + debug_sample_width = debugfs_create_file("width", 0644, + debug_dir, NULL, + &width_fops); + if (!debug_sample_width) + goto err_width; + + debug_threshold = debugfs_create_file("threshold", 0644, + debug_dir, NULL, + &threshold_fops); + if (!debug_threshold) + goto err_threshold; + + debug_enable = debugfs_create_file("enable", 0644, + debug_dir, &enabled, + &enable_fops); + if (!debug_enable) + goto err_enable; + + else { + ret = 0; + goto out; + } + +err_enable: + debugfs_remove(debug_threshold); +err_threshold: + debugfs_remove(debug_sample_width); +err_width: + debugfs_remove(debug_sample_window); +err_window: + debugfs_remove(debug_max); +err_max: + debugfs_remove(debug_count); +err_count: + debugfs_remove(debug_sample); +err_sample: + debugfs_remove(debug_dir); +err_debug_dir: +out: + return ret; +} + +/** + * free_debugfs - A function to cleanup the debugfs file interface + */ +static void free_debugfs(void) +{ + /* could also use a debugfs_remove_recursive */ + debugfs_remove(debug_enable); + debugfs_remove(debug_threshold); + debugfs_remove(debug_sample_width); + debugfs_remove(debug_sample_window); + debugfs_remove(debug_max); + debugfs_remove(debug_count); + debugfs_remove(debug_sample); + debugfs_remove(debug_dir); +} + +/** + * detector_init - Standard module initialization code + */ +static int detector_init(void) +{ + int ret = -ENOMEM; + + printk(KERN_INFO BANNER "version %s\n", VERSION); + + ret = init_stats(); + if (0 != ret) + goto out; + + ret = init_debugfs(); + if (0 != ret) + goto err_stats; + + if (enabled) + ret = start_kthread(); + + goto out; + +err_stats: + ring_buffer_free(ring_buffer); +out: + return ret; + +} + +/** + * detector_exit - Standard module cleanup code + */ +static void detector_exit(void) +{ + int err; + + if (enabled) { + enabled = 0; + err = stop_kthread(); + if (err) + printk(KERN_ERR BANNER "cannot stop kthread\n"); + } + + free_debugfs(); + ring_buffer_free(ring_buffer); /* free up the ring buffer */ + +} + +module_init(detector_init); +module_exit(detector_exit); |