Messages in this thread | | | Date | Sat, 24 Feb 2018 09:41:06 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read from any CPU |
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On Fri, Feb 23, 2018 at 04:19:38PM -0800, Saravana Kannan wrote: > Some PMUs events can be read from any CPU. So allow the PMU to mark > events as such. For these events, we don't need to reject reads or > make smp calls to the event's CPU and cause unnecessary wake ups. > > Good examples of such events would be events from caches shared across > all CPUs.
So why would the existing ACTIVE_PKG not work for you? Because clearly your example does not cross a package.
> Signed-off-by: Saravana Kannan <skannan@codeaurora.org> > --- > include/linux/perf_event.h | 3 +++ > kernel/events/core.c | 10 ++++++++-- > 2 files changed, 11 insertions(+), 2 deletions(-) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 7546822..ee8978f 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -510,9 +510,12 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *, > * PERF_EV_CAP_SOFTWARE: Is a software event. > * PERF_EV_CAP_READ_ACTIVE_PKG: A CPU event (or cgroup event) that can be read > * from any CPU in the package where it is active. > + * PERF_EV_CAP_READ_ANY_CPU: A CPU event (or cgroup event) that can be read > + * from any CPU. > */ > #define PERF_EV_CAP_SOFTWARE BIT(0) > #define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1) > +#define PERF_EV_CAP_READ_ANY_CPU BIT(2) > > #define SWEVENT_HLIST_BITS 8 > #define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS) > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 5d3df58..570187b 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -3484,6 +3484,10 @@ static int __perf_event_read_cpu(struct perf_event *event, int event_cpu) > { > u16 local_pkg, event_pkg; > > + if (event->group_caps & PERF_EV_CAP_READ_ANY_CPU) { > + return smp_processor_id(); > + } > + > if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) { > int local_cpu = smp_processor_id(); >
> @@ -3575,6 +3579,7 @@ int perf_event_read_local(struct perf_event *event, u64 *value, > { > unsigned long flags; > int ret = 0; > + bool is_any_cpu = !!(event->group_caps & PERF_EV_CAP_READ_ANY_CPU); > > /* > * Disabling interrupts avoids all counter scheduling (context > @@ -3600,7 +3605,8 @@ int perf_event_read_local(struct perf_event *event, u64 *value, > > /* If this is a per-CPU event, it must be for this CPU */ > if (!(event->attach_state & PERF_ATTACH_TASK) && > - event->cpu != smp_processor_id()) { > + event->cpu != smp_processor_id() && > + !is_any_cpu) { > ret = -EINVAL; > goto out; > } > @@ -3610,7 +3616,7 @@ int perf_event_read_local(struct perf_event *event, u64 *value, > * or local to this CPU. Furthermore it means its ACTIVE (otherwise > * oncpu == -1). > */ > - if (event->oncpu == smp_processor_id()) > + if (event->oncpu == smp_processor_id() || is_any_cpu) > event->pmu->read(event); > > *value = local64_read(&event->count);
And why are you modifying read_local for this? That didn't support ACTIVE_PKG, so why should it support this?
And again, where are the users?
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