diff options
| -rw-r--r-- | Documentation/trace/hwlat_detector.txt | 6 | ||||
| -rw-r--r-- | kernel/trace/trace_hwlat.c | 55 |
2 files changed, 61 insertions, 0 deletions
diff --git a/Documentation/trace/hwlat_detector.txt b/Documentation/trace/hwlat_detector.txt index c02e8ef800cf..3207717a0d1a 100644 --- a/Documentation/trace/hwlat_detector.txt +++ b/Documentation/trace/hwlat_detector.txt @@ -69,5 +69,11 @@ in /sys/kernel/tracing: tracing_threshold - minimum latency value to be considered (usecs) tracing_max_latency - maximum hardware latency actually observed (usecs) + tracing_cpumask - the CPUs to move the hwlat thread across hwlat_detector/width - specified amount of time to spin within window (usecs) hwlat_detector/window - amount of time between (width) runs (usecs) + +The hwlat detector's kernel thread will migrate across each CPU specified in +tracing_cpumask between each window. To limit the migration, either modify +tracing_cpumask, or modify the hwlat kernel thread (named [hwlatd]) CPU +affinity directly, and the migration will stop. diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c index 08dfabe4e862..65aab3914a56 100644 --- a/kernel/trace/trace_hwlat.c +++ b/kernel/trace/trace_hwlat.c @@ -42,6 +42,7 @@ #include <linux/kthread.h> #include <linux/tracefs.h> #include <linux/uaccess.h> +#include <linux/cpumask.h> #include <linux/delay.h> #include "trace.h" @@ -211,6 +212,57 @@ out: return ret; } +static struct cpumask save_cpumask; +static bool disable_migrate; + +static void move_to_next_cpu(void) +{ + static struct cpumask *current_mask; + int next_cpu; + + if (disable_migrate) + return; + + /* Just pick the first CPU on first iteration */ + if (!current_mask) { + current_mask = &save_cpumask; + get_online_cpus(); + cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask); + put_online_cpus(); + next_cpu = cpumask_first(current_mask); + goto set_affinity; + } + + /* + * If for some reason the user modifies the CPU affinity + * of this thread, than stop migrating for the duration + * of the current test. + */ + if (!cpumask_equal(current_mask, ¤t->cpus_allowed)) + goto disable; + + get_online_cpus(); + cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask); + next_cpu = cpumask_next(smp_processor_id(), current_mask); + put_online_cpus(); + + if (next_cpu >= nr_cpu_ids) + next_cpu = cpumask_first(current_mask); + + set_affinity: + if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */ + goto disable; + + cpumask_clear(current_mask); + cpumask_set_cpu(next_cpu, current_mask); + + sched_setaffinity(0, current_mask); + return; + + disable: + disable_migrate = true; +} + /* * kthread_fn - The CPU time sampling/hardware latency detection kernel thread * @@ -230,6 +282,8 @@ static int kthread_fn(void *data) while (!kthread_should_stop()) { + move_to_next_cpu(); + local_irq_disable(); get_sample(); local_irq_enable(); @@ -473,6 +527,7 @@ static int hwlat_tracer_init(struct trace_array *tr) hwlat_trace = tr; + disable_migrate = false; hwlat_data.count = 0; tr->max_latency = 0; save_tracing_thresh = tracing_thresh; |