Introduce the flag PMU_EV_CAP_READ_ACTIVE_PKG, useful for uncore events, that allows a PMU to signal the generic perf code that an event is readable in the current CPU if the event is active in a CPU in the same package as the current CPU.
This is an optimization that avoids a unnecessary IPI for the common case where uncore events are run and read in the same package but in different CPUs. As an example, the IPI removal speeds up perf_read in my Haswell system as follows: - For event UNC_C_LLC_LOOKUP: From 260 us to 31 us. - For event RAPL's power/energy-cores/: From to 255 us to 27 us. For the optimization to work, all events in the group must have it (similarly to PERF_EV_CAP_SOFTWARE). Signed-off-by: David Carrillo-Cisneros <davi...@google.com> --- include/linux/perf_event.h | 3 +++ kernel/events/core.c | 26 ++++++++++++++++++++++++-- 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index fa5617f..c8bb1b3 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -501,8 +501,11 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *, * Event capabilities. For event_caps and groups caps. * * 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. */ #define PERF_EV_CAP_SOFTWARE BIT(0) +#define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1) #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 34049cc..38ec68d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3333,6 +3333,22 @@ struct perf_read_data { int ret; }; +static int find_cpu_to_read(struct perf_event *event, int local_cpu) +{ + int event_cpu = event->oncpu; + u16 local_pkg, event_pkg; + + if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) { + event_pkg = topology_physical_package_id(event_cpu); + local_pkg = topology_physical_package_id(local_cpu); + + if (event_pkg == local_pkg) + return local_cpu; + } + + return event_cpu; +} + /* * Cross CPU call to read the hardware event */ @@ -3454,7 +3470,7 @@ u64 perf_event_read_local(struct perf_event *event) static int perf_event_read(struct perf_event *event, bool group) { - int ret = 0; + int ret = 0, cpu_to_read, local_cpu; /* * If event is enabled and currently active on a CPU, update the @@ -3466,8 +3482,14 @@ static int perf_event_read(struct perf_event *event, bool group) .group = group, .ret = 0, }; - ret = smp_call_function_single(event->oncpu, + + local_cpu = get_cpu(); + cpu_to_read = find_cpu_to_read(event, local_cpu); + put_cpu(); + + ret = smp_call_function_single(cpu_to_read, __perf_event_read, &data, 1); + ret = ret ? : data.ret; } else if (event->state == PERF_EVENT_STATE_INACTIVE) { struct perf_event_context *ctx = event->ctx; -- 2.8.0.rc3.226.g39d4020