diff options
| author | Song Liu <songliubraving@fb.com> | 2021-09-29 12:43:13 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-10-17 10:43:33 +0200 |
| commit | bdae2a08343613782be6c5be97b6c3a1ebccbfff (patch) | |
| tree | e778eff26dc2349aab2298aeda999c1adb6c3f55 /include/linux | |
| parent | 57c7ca3d5592d153dd5459894ffb63f2a40ac17c (diff) | |
perf/core: fix userpage->time_enabled of inactive events
[ Upstream commit f792565326825ed806626da50c6f9a928f1079c1 ]
Users of rdpmc rely on the mmapped user page to calculate accurate
time_enabled. Currently, userpage->time_enabled is only updated when the
event is added to the pmu. As a result, inactive event (due to counter
multiplexing) does not have accurate userpage->time_enabled. This can
be reproduced with something like:
/* open 20 task perf_event "cycles", to create multiplexing */
fd = perf_event_open(); /* open task perf_event "cycles" */
userpage = mmap(fd); /* use mmap and rdmpc */
while (true) {
time_enabled_mmap = xxx; /* use logic in perf_event_mmap_page */
time_enabled_read = read(fd).time_enabled;
if (time_enabled_mmap > time_enabled_read)
BUG();
}
Fix this by updating userpage for inactive events in merge_sched_in.
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-and-tested-by: Lucian Grijincu <lucian@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210929194313.2398474-1-songliubraving@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/perf_event.h | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 072ac6c1ef2b..c095e713cf08 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -682,7 +682,9 @@ struct perf_event { /* * timestamp shadows the actual context timing but it can * be safely used in NMI interrupt context. It reflects the - * context time as it was when the event was last scheduled in. + * context time as it was when the event was last scheduled in, + * or when ctx_sched_in failed to schedule the event because we + * run out of PMC. * * ctx_time already accounts for ctx->timestamp. Therefore to * compute ctx_time for a sample, simply add perf_clock(). |