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perf: Fix wakeup storm for RO mmap()s

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RO mmap()s don't update the tail pointer, so
comparing against it for determining the written data
size doesn't really do any good.

Keep track of when we last did a wakeup, and compare
against that.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20100521090710.684479310@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2010-05-20 16:21:55 +02:00 committed by Ingo Molnar
parent 0e2e63dd60
commit adb8e118f2
2 changed files with 3 additions and 3 deletions
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2
include/linux/perf_event.h
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@ -599,7 +599,7 @@ struct perf_mmap_data {
local_t head; /* write position */
local_t nest; /* nested writers */
local_t events; /* event limit */
local_t wakeup; /* needs a wakeup */
local_t wakeup; /* wakeup stamp */
local_t lost; /* nr records lost */
long watermark; /* wakeup watermark */

4
kernel/perf_event.c
View File

@ -3056,8 +3056,8 @@ int perf_output_begin(struct perf_output_handle *handle,
handle->offset = offset;
handle->head = head;
if (head - tail > data->watermark)
local_inc(&data->wakeup);
if (head - local_read(&data->wakeup) > data->watermark)
local_add(data->watermark, &data->wakeup);
if (have_lost) {
lost_event.header.type = PERF_RECORD_LOST;