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perf/core: Fix implicitly enable dynamic interrupt throttle

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This patch fixes an issue which was introduced by commit:

  91a612eea9 ("perf/core: Fix dynamic interrupt throttle")

... which commit unconditionally sets the perf_sample_allowed_ns value
to !0. But that could trigger a bug in the following corner case:

The user can disable the dynamic interrupt throttle mechanism by setting
perf_cpu_time_max_percent to 0. Then they change perf_event_max_sample_rate.
For this case, the mechanism will be enabled implicitly, because
perf_sample_allowed_ns becomes !0 - which is not what we want.

This patch only updates perf_sample_allowed_ns when the dynamic
interrupt throttle mechanism is enabled.

Signed-off-by: Kan Liang <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Kan Liang 2016-05-03 00:26:06 -07:00 • committed by Ingo Molnar
commit ab7fdefba6
1 changed files with 7 additions and 0 deletions
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7
kernel/events/core.c
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@ -397,6 +397,13 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
if (ret || !write)
return ret;
/*
* If throttling is disabled don't allow the write:
*/
if (sysctl_perf_cpu_time_max_percent == 100 ||
sysctl_perf_cpu_time_max_percent == 0)
return -EINVAL;
max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
update_perf_cpu_limits();