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Date: Thu, 6 Aug 2015 10:49:26 +0800 From: xiakaixu <xiakaixu@...wei.com> To: Peter Zijlstra <peterz@...radead.org> CC: <ast@...mgrid.com>, <davem@...emloft.net>, <acme@...nel.org>, <mingo@...hat.com>, <masami.hiramatsu.pt@...achi.com>, <jolsa@...nel.org>, <daniel@...earbox.net>, <wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>, <pi3orama@....com>, <hekuang@...wei.com>, <netdev@...r.kernel.org> Subject: Re: [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter δΊ 2015/8/5 21:53, Peter Zijlstra ει: > On Wed, Aug 05, 2015 at 12:04:25PM +0200, Peter Zijlstra wrote: >> Also, you probably want a WARN_ON(in_nmi()) there, this function is >> _NOT_ NMI safe. > > I had a wee think about that, and I think the below is safe. > > (with the obvious problem that WARN from NMI context is not safe) > > It does not give you up-to-date overcommit times but your version didn't > either so I'm assuming you don't need those, if you do need those it > needs more but we can do that too. > > --- > include/linux/perf_event.h | 1 + > kernel/events/core.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 54 insertions(+) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 2027809433b3..64e821dd64f0 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -659,6 +659,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, > void *context); > extern void perf_pmu_migrate_context(struct pmu *pmu, > int src_cpu, int dst_cpu); > +extern u64 perf_event_read_local(struct perf_event *event); > extern u64 perf_event_read_value(struct perf_event *event, > u64 *enabled, u64 *running); > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 39753bfd9520..7105d37763c1 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -3222,6 +3222,59 @@ static inline u64 perf_event_count(struct perf_event *event) > return __perf_event_count(event); > } > > +/* > + * NMI-safe method to read a local event, that is an event that > + * is: > + * - either for the current task, or for this CPU > + * - does not have inherit set, for inherited task events > + * will not be local and we cannot read them atomically > + * - must not have a pmu::count method > + */ > +u64 perf_event_read_local(struct perf_event *event) > +{ > + unsigned long flags; > + u64 val; > + > + /* > + * Disabling interrupts avoids all counter scheduling (context > + * switches, timer based rotation and IPIs). > + */ > + local_irq_safe(flags); s/local_irq_safe/local_irq_save, and I have compiled and tested this function and it is fine. Will use it in the next set. Thanks. > + > + /* If this is a per-task event, it must be for current */ > + WARN_ON_ONCE((event->attach_state & PERF_ATTACH_TASK) && > + event->hw.target != current); > + > + /* If this is a per-CPU event, it must be for this CPU */ > + WARN_ON_ONCE(!(event->attach_state & PERF_ATTACH_TASK) && > + event->cpu != smp_processor_id()); > + > + /* > + * It must not be an event with inherit set, we cannot read > + * all child counters from atomic context. > + */ > + WARN_ON_ONCE(event->attr.inherit); > + > + /* > + * It must not have a pmu::count method, those are not > + * NMI safe. > + */ > + WARN_ON_ONCE(event->pmu->count); > + > + /* > + * If the event is currently on this CPU, its either a per-task event, > + * or local to this CPU. Furthermore it means its ACTIVE (otherwise > + * oncpu == -1). > + */ > + if (event->oncpu == smp_processor_id()) > + event->pmu->read(event); > + > + val = local64_read(&event->count); > + local_irq_restore(flags); > + > + return val; > +} > + > static u64 perf_event_read(struct perf_event *event) > { > /* > > . > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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