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 <skan...@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?
