perf/core: fix implicitly enable dynamic interrupt throttle
PATCH 1/1 perf/core: fix implicitly enable dynamic interrupt throttle
From: Kan Liang <[email protected]>
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.
--- kernel/events/core.c | 8 ++++++++ 1 file changed, 8 insertions(+)
kernel/events/core.c +8 -0
@@ -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 ; + tmp *= sysctl_perf_cpu_time_max_percent; tmp =div_u64 (tmp,100 );if (!tmp)
Signature · 1 line
2.5.0
Peter Zijlstra
maintainerQuoted 26 lines · On Tue, May 03, 2016 at 12:26:06AM -0700, [email protected] wrote:
From: Kan Liang <[email protected]>
This patch fixes an issue which was introduced from 'commit
91a612eea9a3("perf/core: Fix dynamic interrupt throttle")'
The old patch unconditionally sets theperf_sample_allowed_nsvalue to !0. But that could trigger an issue in the following corner case. The user can disable the dynamic interrupt throttle mechanism by settingperf_cpu_time_max_percentto 0. Then they changesperf_event_max_sample_rate.
For this case, the mechanism will be enabled implicitly, becauseperf_sample_allowed_nsbecomes !0.This patch only updates the
perf_sample_allowed_nswhen the dynamic interrupt throttle mechanism is enabled.Signed-off-by Kan Liang <[email protected]>--- kernel/events/core.c | 8 ++++++++ 1 file changed, 8 insertions(+)kernel/events/core.c +0
-0@@ -375,6 +375,14 @@ static void update_perf_cpu_limits(void) {
kernel/events/core.c static void update_perf_cpu_limits(void) · line 385
Quoted 10 lines
kernel/events/core.c +8
-0u64 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(+)
kernel/events/core.c +7 -0
@@ -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 ();
Quoted 6 lines
Hmm, would it not be nicer to simply reject the write instead of silently ignoring it?
Yes, I agree.
Thanks,
Kan
Quoted 25 lines
--- kernel/events/core.c | 7 +++++++ 1 file changed, 7 insertions(+)kernel/events/core.c index renamed from kernel/events/core.c +0
-0
050a290c72c7..0a51a568d4eb100644kernel/events/core.c +7
-0@@ -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();
tip-bot for Kan Liang
merge bot[tip:perf/core] perf/core: Fix implicitly enable dynamic interrupt throttle
In reply to [email protected]perf/core: Fix implicitly enable dynamic interrupt throttle
Commit-ID: ab7fdefba68f66c8523571c3b3a940635d781824 Gitweb: http://git.kernel.org/tip/ab7fdefba68f66c8523571c3b3a940635d781824 Author: Kan Liang <[email protected]> AuthorDate: Tue, 3 May 2016 00:26:06 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Fri, 3 Jun 2016 09:40:16 +0200
perf/core: Fix implicitly enable dynamic interrupt throttle
This patch fixes an issue which was introduced by commit:
91a612eea9a3 ("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.
--- kernel/events/core.c | 7 +++++++ 1 file changed, 7 insertions(+)
kernel/events/core.c +7 -0
@@ -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 ();