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Subject[PATCH V2 05/13] perf/core: output side-band events overhead
Date
From: Kan Liang <kan.liang@intel.com>

Iterating all events which need to receive side-band events also bring
some overhead.

The side-band events overhead PERF_CORE_SB_OVERHEAD is a common overhead
type.

Signed-off-by: Kan Liang <kan.liang@intel.com>
---
include/linux/perf_event.h | 2 ++
include/uapi/linux/perf_event.h | 1 +
kernel/events/core.c | 27 ++++++++++++++++++++++++---
3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 351d321..fe4ca0b 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -765,6 +765,8 @@ struct perf_event_context {
#endif
void *task_ctx_data; /* pmu specific data */
struct rcu_head rcu_head;
+
+ struct perf_overhead_entry sb_overhead;
};

/*
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 355086f..bdf2eec 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1000,6 +1000,7 @@ struct perf_branch_entry {
enum perf_record_overhead_type {
PERF_CORE_OVERHEAD = 0,
PERF_CORE_MUX_OVERHEAD = 0,
+ PERF_CORE_SB_OVERHEAD,

PERF_PMU_OVERHEAD = 20,
PERF_PMU_SAMPLE_OVERHEAD = 20,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 025a19d..85706fb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1830,8 +1830,12 @@ event_sched_out(struct perf_event *event,
if (event->attr.exclusive || !cpuctx->active_oncpu)
cpuctx->exclusive = 0;

- if (log_overhead && cpuctx->mux_overhead.nr)
- perf_log_overhead(event, PERF_CORE_MUX_OVERHEAD, &cpuctx->mux_overhead);
+ if (log_overhead) {
+ if (cpuctx->mux_overhead.nr)
+ perf_log_overhead(event, PERF_CORE_MUX_OVERHEAD, &cpuctx->mux_overhead);
+ if (ctx->sb_overhead.nr)
+ perf_log_overhead(event, PERF_CORE_SB_OVERHEAD, &ctx->sb_overhead);
+ }

perf_pmu_enable(event->pmu);
}
@@ -6131,6 +6135,13 @@ static void perf_iterate_sb_cpu(perf_iterate_f output, void *data)
}
}

+static void
+perf_calculate_sb_overhead(struct perf_event_context *ctx, u64 time)
+{
+ ctx->sb_overhead.nr++;
+ ctx->sb_overhead.time += time;
+}
+
/*
* Iterate all events that need to receive side-band events.
*
@@ -6141,9 +6152,12 @@ static void
perf_iterate_sb(perf_iterate_f output, void *data,
struct perf_event_context *task_ctx)
{
+ struct perf_event_context *overhead_ctx = task_ctx;
struct perf_event_context *ctx;
+ u64 start_clock, end_clock;
int ctxn;

+ start_clock = perf_clock();
rcu_read_lock();
preempt_disable();

@@ -6161,12 +6175,19 @@ perf_iterate_sb(perf_iterate_f output, void *data,

for_each_task_context_nr(ctxn) {
ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
- if (ctx)
+ if (ctx) {
perf_iterate_ctx(ctx, output, data, false);
+ if (!overhead_ctx)
+ overhead_ctx = ctx;
+ }
}
done:
preempt_enable();
rcu_read_unlock();
+
+ end_clock = perf_clock();
+ if (overhead_ctx)
+ perf_calculate_sb_overhead(overhead_ctx, end_clock - start_clock);
}

/*
--
2.5.5
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