From: Kan Liang kan.liang@linux.intel.com
[ Upstream commit 35d1ce6bec133679ff16325d335217f108b84871 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/events/intel/ds.c | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index dc43cc124e096..221d1766d6e6c 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -670,9 +670,7 @@ int intel_pmu_drain_bts_buffer(void)
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)