diff options
author | Kan Liang <kan.liang@linux.intel.com> | 2020-09-02 14:06:49 -0700 |
---|---|---|
committer | Peter Zijlstra <peterz@infradead.org> | 2020-09-10 11:19:33 +0200 |
commit | 35d1ce6bec133679ff16325d335217f108b84871 (patch) | |
tree | e11e31fc99b3e93799a6e0a947f41ca31e97d98b /arch/x86/events | |
parent | 2cb5383b30d47c446ec7d884cd80f93ffcc31817 (diff) |
perf/x86/intel/ds: Fix x86_pmu_stop warning for large PEBS
A warning as below may be triggered when sampling with large PEBS.
[ 410.411250] perf: interrupt took too long (72145 > 71975), lowering
kernel.perf_event_max_sample_rate to 2000
[ 410.724923] ------------[ cut here ]------------
[ 410.729822] WARNING: CPU: 0 PID: 16397 at arch/x86/events/core.c:1422
x86_pmu_stop+0x95/0xa0
[ 410.933811] x86_pmu_del+0x50/0x150
[ 410.937304] event_sched_out.isra.0+0xbc/0x210
[ 410.941751] group_sched_out.part.0+0x53/0xd0
[ 410.946111] ctx_sched_out+0x193/0x270
[ 410.949862] __perf_event_task_sched_out+0x32c/0x890
[ 410.954827] ? set_next_entity+0x98/0x2d0
[ 410.958841] __schedule+0x592/0x9c0
[ 410.962332] schedule+0x5f/0xd0
[ 410.965477] exit_to_usermode_loop+0x73/0x120
[ 410.969837] prepare_exit_to_usermode+0xcd/0xf0
[ 410.974369] ret_from_intr+0x2a/0x3a
[ 410.977946] RIP: 0033:0x40123c
[ 411.079661] ---[ end trace bc83adaea7bb664a ]---
In the non-overflow context, e.g., context switch, with large PEBS, perf
may stop an event twice. An example is below.
//max_samples_per_tick is adjusted to 2
//NMI is triggered
intel_pmu_handle_irq()
handle_pmi_common()
drain_pebs()
__intel_pmu_pebs_event()
perf_event_overflow()
__perf_event_account_interrupt()
hwc->interrupts = 1
return 0
//A context switch happens right after the NMI.
//In the same tick, the perf_throttled_seq is not changed.
perf_event_task_sched_out()
perf_pmu_sched_task()
intel_pmu_drain_pebs_buffer()
__intel_pmu_pebs_event()
perf_event_overflow()
__perf_event_account_interrupt()
++hwc->interrupts >= max_samples_per_tick
return 1
x86_pmu_stop(); # First stop
perf_event_context_sched_out()
task_ctx_sched_out()
ctx_sched_out()
event_sched_out()
x86_pmu_del()
x86_pmu_stop(); # Second stop and trigger the warning
Perf should only invoke the perf_event_overflow() in the overflow
context.
Current drain_pebs() is called from:
- handle_pmi_common() -- overflow context
- intel_pmu_pebs_sched_task() -- non-overflow context
- intel_pmu_pebs_disable() -- non-overflow context
- intel_pmu_auto_reload_read() -- possible overflow context
With PERF_SAMPLE_READ + PERF_FORMAT_GROUP, the function may be
invoked in the NMI handler. But, before calling the function, the
PEBS buffer has already been drained. The __intel_pmu_pebs_event()
will not be called in the possible overflow context.
To fix the issue, an indicator is required to distinguish between the
overflow context aka handle_pmi_common() and other cases.
The dummy regs pointer can be used as the indicator.
In the non-overflow context, perf should treat the last record the same
as other PEBS records, and doesn't invoke the generic overflow handler.
Fixes: 21509084f999 ("perf/x86/intel: Handle multiple records in the PEBS buffer")
Reported-by: Like Xu <like.xu@linux.intel.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Like Xu <like.xu@linux.intel.com>
Link: https://lkml.kernel.org/r/20200902210649.2743-1-kan.liang@linux.intel.com
Diffstat (limited to 'arch/x86/events')
-rw-r--r-- | arch/x86/events/intel/ds.c | 32 |
1 files changed, 20 insertions, 12 deletions
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index 86848c57b55e..404315df1e16 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -670,9 +670,7 @@ unlock: static inline void intel_pmu_drain_pebs_buffer(void) { - struct pt_regs regs; - - x86_pmu.drain_pebs(®s); + x86_pmu.drain_pebs(NULL); } /* @@ -1737,6 +1735,7 @@ static void __intel_pmu_pebs_event(struct perf_event *event, struct x86_perf_regs perf_regs; struct pt_regs *regs = &perf_regs.regs; void *at = get_next_pebs_record_by_bit(base, top, bit); + struct pt_regs dummy_iregs; if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) { /* @@ -1749,6 +1748,9 @@ static void __intel_pmu_pebs_event(struct perf_event *event, } else if (!intel_pmu_save_and_restart(event)) return; + if (!iregs) + iregs = &dummy_iregs; + while (count > 1) { setup_sample(event, iregs, at, &data, regs); perf_event_output(event, &data, regs); @@ -1758,16 +1760,22 @@ static void __intel_pmu_pebs_event(struct perf_event *event, } setup_sample(event, iregs, at, &data, regs); - - /* - * All but the last records are processed. - * The last one is left to be able to call the overflow handler. - */ - if (perf_event_overflow(event, &data, regs)) { - x86_pmu_stop(event, 0); - return; + if (iregs == &dummy_iregs) { + /* + * The PEBS records may be drained in the non-overflow context, + * e.g., large PEBS + context switch. Perf should treat the + * last record the same as other PEBS records, and doesn't + * invoke the generic overflow handler. + */ + perf_event_output(event, &data, regs); + } else { + /* + * All but the last records are processed. + * The last one is left to be able to call the overflow handler. + */ + if (perf_event_overflow(event, &data, regs)) + x86_pmu_stop(event, 0); } - } static void intel_pmu_drain_pebs_core(struct pt_regs *iregs) |