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perf/core: Introduce PMU_EV_CAP_READ_ACTIVE_PKG
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 <davidcc@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: David Carrillo-Cisneros <davidcc@google.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Kan Liang <kan.liang@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vegard Nossum <vegard.nossum@gmail.com> Cc: Vince Weaver <vincent.weaver@maine.edu> Link: http://lkml.kernel.org/r/1471467307-61171-4-git-send-email-davidcc@google.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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2 changed files with 26 additions and 2 deletions
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@ -514,8 +514,11 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *,
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* Event capabilities. For event_caps and groups caps.
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*
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* PERF_EV_CAP_SOFTWARE: Is a software event.
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* PERF_EV_CAP_READ_ACTIVE_PKG: A CPU event (or cgroup event) that can be read
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* from any CPU in the package where it is active.
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*/
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#define PERF_EV_CAP_SOFTWARE BIT(0)
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#define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1)
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#define SWEVENT_HLIST_BITS 8
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#define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)
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@ -3424,6 +3424,22 @@ struct perf_read_data {
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int ret;
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};
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static int find_cpu_to_read(struct perf_event *event, int local_cpu)
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{
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int event_cpu = event->oncpu;
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u16 local_pkg, event_pkg;
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if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
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event_pkg = topology_physical_package_id(event_cpu);
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local_pkg = topology_physical_package_id(local_cpu);
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if (event_pkg == local_pkg)
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return local_cpu;
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}
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return event_cpu;
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}
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/*
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* Cross CPU call to read the hardware event
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*/
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@ -3545,7 +3561,7 @@ u64 perf_event_read_local(struct perf_event *event)
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static int perf_event_read(struct perf_event *event, bool group)
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{
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int ret = 0;
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int ret = 0, cpu_to_read, local_cpu;
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/*
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* If event is enabled and currently active on a CPU, update the
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@ -3557,7 +3573,12 @@ static int perf_event_read(struct perf_event *event, bool group)
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.group = group,
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.ret = 0,
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};
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ret = smp_call_function_single(event->oncpu, __perf_event_read, &data, 1);
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local_cpu = get_cpu();
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cpu_to_read = find_cpu_to_read(event, local_cpu);
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put_cpu();
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ret = smp_call_function_single(cpu_to_read, __perf_event_read, &data, 1);
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/* The event must have been read from an online CPU: */
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WARN_ON_ONCE(ret);
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ret = ret ? : data.ret;
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