Messages in this thread Patch in this message | | | Date | Thu, 12 May 2016 11:31:27 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/1] perf/core: fix implicitly enable dynamic interrupt throttle |
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On Tue, May 03, 2016 at 12:26:06AM -0700, kan.liang@intel.com wrote: > From: Kan Liang <kan.liang@intel.com> > > This patch fixes an issue which was introduced from 'commit 91a612eea9a3 > ("perf/core: Fix dynamic interrupt throttle")' > The old patch unconditionally sets the perf_sample_allowed_ns value to > !0. But that could trigger an issue 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 changes > perf_event_max_sample_rate. > For this case, the mechanism will be enabled implicitly, because > perf_sample_allowed_ns becomes !0. > > This patch only updates the perf_sample_allowed_ns when the dynamic > interrupt throttle mechanism is enabled. > > Signed-off-by: Kan Liang <kan.liang@intel.com> > --- > kernel/events/core.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 4e2ebf6..4042a3d 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -375,6 +375,14 @@ static void update_perf_cpu_limits(void) > { > u64 tmp = perf_sample_period_ns; > > + /* > + * Don't update the perf_sample_allowed_ns, > + * if the dynamic interrupt throttle mechanism is disabled. > + */ > + if (sysctl_perf_cpu_time_max_percent == 100 || > + sysctl_perf_cpu_time_max_percent == 0) > + return; > +
Hmm, would it not be nicer to simply reject the write instead of silently ignoring it?
--- kernel/events/core.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 050a290c72c7..0a51a568d4eb 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -396,6 +396,13 @@ int perf_proc_update_handler(struct ctl_table *table, int write, if (ret || !write) return ret; + /* + * If the 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();
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