The following commit has been merged into the perf/core branch of tip:
Commit-ID: 15def34e2635ab7e0e96f1bc32e1b69609f14942
Gitweb: https://git.kernel.org/tip/15def34e2635ab7e0e96f1bc32e1b69609f14942
Author: Yang Jihong <yangjihong1@xxxxxxxxxx>
AuthorDate: Mon, 27 Feb 2023 10:35:08 +08:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 14 Apr 2023 16:08:22 +02:00
perf/core: Fix hardlockup failure caused by perf throttle
commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
introduces a change in throttling threshold judgment. Before this,
compare hwc->interrupts and max_samples_per_tick, then increase
hwc->interrupts by 1, but this commit reverses order of these two
behaviors, causing the semantics of max_samples_per_tick to change.
In literal sense of "max_samples_per_tick", if hwc->interrupts ==
max_samples_per_tick, it should not be throttled, therefore, the judgment
condition should be changed to "hwc->interrupts > max_samples_per_tick".
In fact, this may cause the hardlockup to fail, The minimum value of
max_samples_per_tick may be 1, in this case, the return value of
__perf_event_account_interrupt function is 1.
As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
architecture as an example, see x86_pmu_handle_irq).
Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20230227023508.102230-1-yangjihong1@xxxxxxxxxx
---
kernel/events/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index fb3e436..82b95b8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9433,8 +9433,8 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
hwc->interrupts = 1;
} else {
hwc->interrupts++;
- if (unlikely(throttle
- && hwc->interrupts >= max_samples_per_tick)) {
+ if (unlikely(throttle &&
+ hwc->interrupts > max_samples_per_tick)) {
__this_cpu_inc(perf_throttled_count);
tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
hwc->interrupts = MAX_INTERRUPTS;
|