From: Kan Liang <kan.li...@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.li...@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;
+
tmp *= sysctl_perf_cpu_time_max_percent;
tmp = div_u64(tmp, 100);
if (!tmp)
--
2.5.0
