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Subject[PATCHv2] perf/x86/intel: Account interrupts for PEBS errors
On Wed, Dec 14, 2016 at 08:32:39PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 14, 2016 at 07:16:36PM +0100, Jiri Olsa wrote:
>
> > > > +++ b/arch/x86/events/intel/ds.c
> > > > @@ -1389,9 +1389,13 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs)
> > > > continue;
> > > >
> > > > /* log dropped samples number */
> > > > - if (error[bit])
> > > > + if (error[bit]) {
> > > > perf_log_lost_samples(event, error[bit]);
> > > >
> > > > + if (perf_event_account_interrupt(event, 1))
> > >
> > > Seems a bit daft to expose the .throttle argument, since that would be
> > > the only point of calling this.
> >
> > there's also the other caller from __perf_event_overflow
>
> See the below patchlet ;-)
>
> > > > +static int __perf_event_overflow(struct perf_event *event,
> > > > + int throttle, struct perf_sample_data *data,
> > > > + struct pt_regs *regs)
> > > > +{
> > > > + int events = atomic_read(&event->event_limit);
> > > > + struct hw_perf_event *hwc = &event->hw;
> > > > + int ret = 0;
> > > > +
> > > > + /*
> > > > + * Non-sampling counters might still use the PMI to fold short
> > > > + * hardware counters, ignore those.
> > > > + */
> > > > + if (unlikely(!is_sampling_event(event)))
> > > > + return 0;
> > > > +
> > > > + ret = perf_event_account_interrupt(event, throttle);
> > > > +
> > > > if (event->attr.freq) {
> > > > u64 now = perf_clock();
> > > > s64 delta = now - hwc->freq_time_stamp;
> > >
> > > Arguably, everything in __perf_event_overflow() except for calling of
> > > ->overflow_handler() should be done I think.
> >
> > well, I was wondering about that period adjustment bit
> >
> > but I wasn't sure about those pending_kill/pending_wakeup bits,
> > they make sense to me only if we have some data to deliver
>
> Hmm, maybe. Please add a comment, that way we can at least rediscover we
> thought about this.
>

new version with full changelog

jirka


---
It's possible to setup PEBS events and get only errors and not
a single data, like on SNB-X (model 45) and IVB-EP (model 62)
via 2 perf commands running simultaneously:

taskset -c 1 ./perf record -c 4 -e branches:pp -j any -C 10

This leads to soft lock up, because the error path of the
intel_pmu_drain_pebs_nhm does not account event->hw.interrupt
for error PEBS interrupts so the event is not eventually
stopped when it gets over the max_samples_per_tick limit.

NMI watchdog: BUG: soft lockup - CPU#22 stuck for 22s! [perf_fuzzer:5816]
...
task: ffff880273148000 task.stack: ffffc90002d58000
RIP: 0010:[<ffffffff81159232>] [<ffffffff81159232>] smp_call_function_single+0xe2/0x140
RSP: 0018:ffffc90002d5bd60 EFLAGS: 00000202
...
Call Trace:
? trace_hardirqs_on_caller+0xf5/0x1b0
? perf_cgroup_attach+0x70/0x70
perf_install_in_context+0x199/0x1b0
? ctx_resched+0x90/0x90
SYSC_perf_event_open+0x641/0xf90
SyS_perf_event_open+0x9/0x10
do_syscall_64+0x6c/0x1f0
entry_SYSCALL64_slow_path+0x25/0x25

Adding perf_event_account_interrupt with event's interrupt
and frequency checks and calling it from drain_pebs's error
path.

Keeping pending_kill and pending_wakeup check up logic only
in __perf_event_overflow path, because they make sense only
in case if there's any data to deliver.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
arch/x86/events/intel/ds.c | 6 +++++-
include/linux/perf_event.h | 1 +
kernel/events/core.c | 47 ++++++++++++++++++++++++++++++----------------
3 files changed, 37 insertions(+), 17 deletions(-)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index be202390bbd3..9dfeeeca0ea8 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1389,9 +1389,13 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs)
continue;

/* log dropped samples number */
- if (error[bit])
+ if (error[bit]) {
perf_log_lost_samples(event, error[bit]);

+ if (perf_event_account_interrupt(event))
+ x86_pmu_stop(event, 0);
+ }
+
if (counts[bit]) {
__intel_pmu_pebs_event(event, iregs, base,
top, bit, counts[bit]);
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4741ecdb9817..78ed8105e64d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1259,6 +1259,7 @@ extern void perf_event_disable(struct perf_event *event);
extern void perf_event_disable_local(struct perf_event *event);
extern void perf_event_disable_inatomic(struct perf_event *event);
extern void perf_event_task_tick(void);
+extern int perf_event_account_interrupt(struct perf_event *event);
#else /* !CONFIG_PERF_EVENTS: */
static inline void *
perf_aux_output_begin(struct perf_output_handle *handle,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 02c8421f8c01..7c6264f5deb7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7034,25 +7034,11 @@ static void perf_log_itrace_start(struct perf_event *event)
perf_output_end(&handle);
}

-/*
- * Generic event overflow handling, sampling.
- */
-
-static int __perf_event_overflow(struct perf_event *event,
- int throttle, struct perf_sample_data *data,
- struct pt_regs *regs)
+static int __perf_event_account_interrupt(struct perf_event *event, int throttle)
{
- int events = atomic_read(&event->event_limit);
struct hw_perf_event *hwc = &event->hw;
- u64 seq;
int ret = 0;
-
- /*
- * Non-sampling counters might still use the PMI to fold short
- * hardware counters, ignore those.
- */
- if (unlikely(!is_sampling_event(event)))
- return 0;
+ u64 seq;

seq = __this_cpu_read(perf_throttled_seq);
if (seq != hwc->interrupts_seq) {
@@ -7080,6 +7066,35 @@ static int __perf_event_overflow(struct perf_event *event,
perf_adjust_period(event, delta, hwc->last_period, true);
}

+ return ret;
+}
+
+int perf_event_account_interrupt(struct perf_event *event)
+{
+ return __perf_event_account_interrupt(event, 1);
+}
+
+/*
+ * Generic event overflow handling, sampling.
+ */
+
+static int __perf_event_overflow(struct perf_event *event,
+ int throttle, struct perf_sample_data *data,
+ struct pt_regs *regs)
+{
+ int events = atomic_read(&event->event_limit);
+ struct hw_perf_event *hwc = &event->hw;
+ int ret = 0;
+
+ /*
+ * Non-sampling counters might still use the PMI to fold short
+ * hardware counters, ignore those.
+ */
+ if (unlikely(!is_sampling_event(event)))
+ return 0;
+
+ ret = __perf_event_account_interrupt(event, throttle);
+
/*
* XXX event_limit might not quite work as expected on inherited
* events
--
2.7.4
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