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perf_counter: Allow for a wakeup watermark

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Currently we wake the mmap() consumer once every PAGE_SIZE of data
and/or once event wakeup_events when specified.

For high speed sampling this results in too many wakeups wrt. the
buffer size, hence change this.

We move the default wakeup limit to 1/4-th the buffer size, and
provide for means to manually specify this limit.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-09-17 19:01:10 +02:00 • committed by Ingo Molnar
parent 850bc73ffc
commit 2667de81f3
2 changed files with 27 additions and 15 deletions
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10
include/linux/perf_counter.h
View file

@ -199,10 +199,14 @@ struct perf_counter_attr {
inherit_stat : 1, /* per task counts */
enable_on_exec : 1, /* next exec enables */
task : 1, /* trace fork/exit */
watermark : 1, /* wakeup_watermark */
__reserved_1 : 50;
__reserved_1 : 49;
__u32 wakeup_events; /* wakeup every n events */
union {
__u32 wakeup_events; /* wakeup every n events */
__u32 wakeup_watermark; /* bytes before wakeup */
};
__u32 __reserved_2;
__u64 __reserved_3;
@ -521,6 +525,8 @@ struct perf_mmap_data {
atomic_t wakeup; /* needs a wakeup */
atomic_t lost; /* nr records lost */
long watermark; /* wakeup watermark */
struct perf_counter_mmap_page *user_page;
void *data_pages[0];
};