Messages in this thread | | | Date | Mon, 26 Feb 2018 17:53:57 -0800 | From | skannan@codeauro ... | Subject | Re: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read from any CPU |
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On 2018-02-24 00:41, Peter Zijlstra wrote: > 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.
Because based on testing it on hardware, it looks like the two clusters in an ARM DynamIQ design are not considered part of the same "package". When I say clusters, I using the more common interpretation of "homogeneous CPUs running on the same clock"/CPUs in a cpufreq policy and not ARM's new redefinition of cluster. So, on a SoC with 4 little and 4 big cores, it'll still trigger a lot of unnecessary smp calls/IPIs that cause unnecessary wakeups.
Although, I like Mark's suggestion of just giving a cpumask for every event and using that instead. Because the meaning of "active package" is very ambiguous. For example if a SoC has 2 DynamIQ blocks (not sure if that's possible), what's considered a package? CPUs that are sitting on one L3 can't read the PMU counters of a different L3. In that case, neither "Any CPU" nor "Active Package" is correct/usable for reducing IPIs.
> >> 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?
Maybe I'll make a separate patch to first have perf_event_read_local() also handle ACTIVE_PACKAGE? Because in those cases, the smp call made by read_local is unnecessary too.
> > And again, where are the users?
The DynamIQ PMU driver would be the user.
-Saravana
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