linux-toradex.git/kernel/trace/ring_buffer_benchmark.c, branch v3.15-rc8

trace: Replace hardcoding of 19 with MAX_NICE

2014-02-27T11:41:03+00:00

Use MAX_NICE instead of the value 19 for ring_buffer_benchmark.

Signed-off-by: Dongsheng Yang 
Signed-off-by: Peter Zijlstra 
Acked-by: Steven Rostedt 
Cc: Frederic Weisbecker 
Link: http://lkml.kernel.org/r/1393251121-25534-1-git-send-email-yangds.fnst@cn.fujitsu.com
Signed-off-by: Ingo Molnar

tracing: Use NUMA allocation for per-cpu ring buffer pages

2011-06-15T02:04:39+00:00

The tracing ring buffer is a group of per-cpu ring buffers where
allocation and logging is done on a per-cpu basis. The events that are
generated on a particular CPU are logged in the corresponding buffer.
This is to provide wait-free writes between CPUs and good NUMA node
locality while accessing the ring buffer.

However, the allocation routines consider NUMA locality only for buffer
page metadata and not for the actual buffer page. This causes the pages
to be allocated on the NUMA node local to the CPU where the allocation
routine is running at the time.

This patch fixes the problem by using a NUMA node specific allocation
routine so that the pages are allocated from a NUMA node local to the
logging CPU.

I tested with the getuid_microbench from autotest. It is a simple binary
that calls getuid() in a loop and measures the average time for the
syscall to complete. The following command was used to test:
$ getuid_microbench 1000000

Compared the numbers found on kernel with and without this patch and
found that logging latency decreases by 30-50 ns/call.
tracing with non-NUMA allocation - 569 ns/call
tracing with NUMA allocation     - 512 ns/call

Signed-off-by: Vaibhav Nagarnaik 
Cc: Frederic Weisbecker 
Cc: Ingo Molnar 
Cc: Michael Rubin 
Cc: David Sharp 
Link: http://lkml.kernel.org/r/1304470602-20366-1-git-send-email-vnagarnaik@google.com
Signed-off-by: Steven Rostedt

ring-buffer: Make benchmark handle missed events

2010-04-27T17:26:58+00:00

With the addition of the "missed events" flags that is stored in the
commit field of the ring buffer page, the ring_buffer_benchmark
was not updated to handle this. If events are missed, then the
missed events flag is set in the ring buffer page, the benchmark
will count that flag as part of the size of the page and will hit the BUG()
when it tries to read beyond the page.

The solution is simply to have the ring buffer benchmark mask off
the extra bits.

Reported-by: Ingo Molnar 
Signed-off-by: Steven Rostedt

ring-buffer: Add place holder recording of dropped events

2010-04-01T02:57:04+00:00

Currently, when the ring buffer drops events, it does not record
the fact that it did so. It does inform the writer that the event
was dropped by returning a NULL event, but it does not put in any
place holder where the event was dropped.

This is not a trivial thing to add because the ring buffer mostly
runs in overwrite (flight recorder) mode. That is, when the ring
buffer is full, new data will overwrite old data.

In a produce/consumer mode, where new data is simply dropped when
the ring buffer is full, it is trivial to add the placeholder
for dropped events. When there's more room to write new data, then
a special event can be added to notify the reader about the dropped
events.

But in overwrite mode, any new write can overwrite events. A place
holder can not be inserted into the ring buffer since there never
may be room. A reader could also come in at anytime and miss the
placeholder.

Luckily, the way the ring buffer works, the read side can find out
if events were lost or not, and how many events. Everytime a write
takes place, if it overwrites the header page (the next read) it
updates a "overrun" variable that keeps track of the number of
lost events. When a reader swaps out a page from the ring buffer,
it can record this number, perfom the swap, and then check to
see if the number changed, and take the diff if it has, which would be
the number of events dropped. This can be stored by the reader
and returned to callers of the reader.

Since the reader page swap will fail if the writer moved the head
page since the time the reader page set up the swap, this gives room
to record the overruns without worrying about races. If the reader
sets up the pages, records the overrun, than performs the swap,
if the swap succeeds, then the overrun variable has not been
updated since the setup before the swap.

For binary readers of the ring buffer, a flag is set in the header
of each sub page (sub buffer) of the ring buffer. This flag is embedded
in the size field of the data on the sub buffer, in the 31st bit (the size
can be 32 or 64 bits depending on the architecture), but only 27
bits needs to be used for the actual size (less actually).

We could add a new field in the sub buffer header to also record the
number of events dropped since the last read, but this will change the
format of the binary ring buffer a bit too much. Perhaps this change can
be made if the information on the number of events dropped is considered
important enough.

Note, the notification of dropped events is only used by consuming reads
or peeking at the ring buffer. Iterating over the ring buffer does not
keep this information because the necessary data is only available when
a page swap is made, and the iterator does not swap out pages.

Cc: Robert Richter 
Cc: Andi Kleen 
Cc: Li Zefan 
Cc: Arnaldo Carvalho de Melo 
Cc: "Luis Claudio R. Goncalves" 
Cc: Frederic Weisbecker 
Signed-off-by: Steven Rostedt

local_t: Move local.h include to ringbuffer.c and ring_buffer_benchmark.c

2010-01-05T06:34:50+00:00

ringbuffer*.c are the last users of local.h.

Remove the include from modules.h and add it to ringbuffer files.

Signed-off-by: Christoph Lameter 
Signed-off-by: Tejun Heo

ring-buffer-benchmark: Add parameters to set produce/consumer priorities

2009-11-25T19:14:15+00:00

Running the ring-buffer-benchmark's threads at the lowest priority may
work well for keeping it in the background, but it is not appropriate
for the benchmarks.

This patch adds 4 parameters to the module:

  consumer_fifo
  consumer_nice
  producer_fifo
  producer_nice

By default the consumer and producer still run at nice +19.

If the *_fifo options are set, they will override the *_nice values.

 modprobe ring_buffer_benchmark consumer_nice=0 producer_fifo=10

The above will set the consumer thread to a nice value of 0, and
the producer thread to a RT SCHED_FIFO priority of 10.

Note, this patch also fixes a bug where calling set_user_nice on the
consumer thread would oops the kernel when the parameter "disable_reader"
is set.

Signed-off-by: Steven Rostedt

ring-buffer benchmark: Run producer/consumer threads at nice +19

2009-11-23T07:03:09+00:00

The ring-buffer benchmark threads run on nice 0 by default, using
up a lot of CPU time and slowing down the system:

   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  1024 root      20   0     0    0    0 D 95.3  0.0   4:01.67 rb_producer
  1023 root      20   0     0    0    0 R 93.5  0.0   2:54.33 rb_consumer
 21569 mingo     40   0 14852 1048  772 R  3.6  0.1   0:00.05 top
     1 root      40   0  4080  928  668 S  0.0  0.0   0:23.98 init

Renice them to +19 to make them less intrusive.

Cc: Steven Rostedt 
Cc: Frederic Weisbecker 
Cc: Peter Zijlstra 
Cc: Mike Galbraith 
LKML-Reference: 
Signed-off-by: Ingo Molnar

ring-buffer: Add multiple iterations between benchmark timestamps

2009-11-12T03:22:15+00:00

The ring_buffer_benchmark does a gettimeofday after every write to the
ring buffer in its measurements. This adds the overhead of the call
to gettimeofday to the measurements and does not give an accurate picture
of the length of time it takes to record a trace.

This was first noticed with perf top:

------------------------------------------------------------------------------
   PerfTop:     679 irqs/sec  kernel:99.9% [1000Hz cpu-clock-msecs],  (all, 4 CPUs)
------------------------------------------------------------------------------

             samples    pcnt   kernel function
             _______   _____   _______________

             1673.00 - 27.8% : trace_clock_local
              806.00 - 13.4% : do_gettimeofday
              590.00 -  9.8% : rb_reserve_next_event
              554.00 -  9.2% : native_read_tsc
              431.00 -  7.2% : ring_buffer_lock_reserve
              365.00 -  6.1% : __rb_reserve_next
              355.00 -  5.9% : rb_end_commit
              322.00 -  5.4% : getnstimeofday
              268.00 -  4.5% : ring_buffer_unlock_commit
              262.00 -  4.4% : ring_buffer_producer_thread 	[ring_buffer_benchmark]
              113.00 -  1.9% : read_tsc
               91.00 -  1.5% : debug_smp_processor_id
               69.00 -  1.1% : trace_recursive_unlock
               66.00 -  1.1% : ring_buffer_event_data
               25.00 -  0.4% : _spin_unlock_irq

And the length of each write to the ring buffer measured at 310ns.

This patch adds a new module parameter called "write_interval" which is
defaulted to 50. This is the number of writes performed between
timestamps. After this patch perf top shows:

------------------------------------------------------------------------------
   PerfTop:     244 irqs/sec  kernel:100.0% [1000Hz cpu-clock-msecs],  (all, 4 CPUs)
------------------------------------------------------------------------------

             samples    pcnt   kernel function
             _______   _____   _______________

             2842.00 - 40.4% : trace_clock_local
             1043.00 - 14.8% : rb_reserve_next_event
              784.00 - 11.1% : ring_buffer_lock_reserve
              600.00 -  8.5% : __rb_reserve_next
              579.00 -  8.2% : rb_end_commit
              440.00 -  6.3% : ring_buffer_unlock_commit
              290.00 -  4.1% : ring_buffer_producer_thread 	[ring_buffer_benchmark]
              155.00 -  2.2% : debug_smp_processor_id
              117.00 -  1.7% : trace_recursive_unlock
              103.00 -  1.5% : ring_buffer_event_data
               28.00 -  0.4% : do_gettimeofday
               22.00 -  0.3% : _spin_unlock_irq
               14.00 -  0.2% : native_read_tsc
               11.00 -  0.2% : getnstimeofday

do_gettimeofday dropped from 13% usage to a mere 0.4%! (using the default
50 interval)  The measurement for each timestamp went from 310ns to 210ns.
That's 100ns (1/3rd) overhead that the gettimeofday call was introducing.

Signed-off-by: Steven Rostedt

ring-buffer: have benchmark test print to trace buffer

2009-06-17T21:01:09+00:00

Currently the output of the ring buffer benchmark/test prints to
the console. This test runs for ten seconds every ten seconds and
ouputs the result after every iteration. This needlessly fills up
the logs.

This patch makes the ring buffer benchmark/test print to the ftrace
buffer using trace_printk. To view the test results, you must examine
the debug/tracing/trace file.

Signed-off-by: Steven Rostedt

ring-buffer: have benchmark test handle discarded events

2009-06-16T17:48:52+00:00

With the addition of commit:

  c7b0930857e2278f2e7714db6294e94c57f623b0
  ring-buffer: prevent adding write in discarded area

The ring buffer may now add discarded events when a write passes
the end of a buffer page. Before, a discarded event was only added
when the tracer deliberately created one. The ring buffer benchmark
test does not handle discarded events when it reads the buffer and
fails when it encounters one.

Also fix the increment for large data entries (luckily, the test did
not add any yet).

[ Impact: fix false failure of ring buffer self test ]

Signed-off-by: Steven Rostedt