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SubjectRe: [RFC] perf/core: what is exclude_idle supposed to do
On Mon, Apr 16, 2018 at 10:04:53PM +0000, Stephane Eranian wrote:
> Hi,
>
> I am trying to understand what the exclude_idle event attribute is supposed
> to accomplish.
> As per the definition in the header file:
>
> exclude_idle : 1, /* don't count when idle */
>
> Naively, I thought it would simply stop the event when running in the
> context of the idle task (swapper, pid 0) on any CPU. That would seem to
> match the succinct description.
>
> However, running a simple:
>
> $ perf record -a -e cycles:I sleep 5
> perf_event_attr:
> sample_type IP|TID|TIME|CPU|PERIOD
> read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING|ID
> exclude_idle 1
>
> on an idle machine, showed me that this is not what is actually happening:
> $ perf script
> swapper 0 [000] 1132634.287442: 1 cycles:I:
> ffffffff8100b1fb __intel_pmu_enable_all.isra.17 ([kernel.kallsyms])
> swapper 0 [001] 1132634.287498: 1 cycles:I:
> ffffffff8100b1fb __intel_pmu_enable_all.isra.17 ([kernel.kallsyms])
>
>
> After looking at the code, it all made sense, it seems to current
> implementation is only relevant for sw events. I don't understand why.

AFAICS it's not implemented

Peter suggested some time ago change for cpu-clock (attached)
I still have it in my queue, because it gives funny numbers
sometimes.. and I haven't figured it out so far

the idea so far was to use cpu-clock,cpu-clock:I events to
count and display idle % in perf top/record and stat metrics

jirka


---
From 7f20b047cf56f8086d79007175592633798656ce Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Thu, 23 Nov 2017 16:15:36 +0100
Subject: [PATCH] perf: Add support to monitor idle time on cpu-clock

Adding support to use perf_event_attr::exclude_idle
(the :I modifierr in perf tools)to monitor idle time
on cpu-clock event.

Link: http://lkml.kernel.org/n/tip-jw45kl6ydrhzqx4uxws0qsqb@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
kernel/events/core.c | 22 ++++++++++++++++++----
kernel/sched/idle_task.c | 17 +++++++++++++++++
2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2989e3b0fe8b..62c0dc75ed11 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9391,19 +9391,33 @@ static void perf_swevent_init_hrtimer(struct perf_event *event)
* Software event: cpu wall time clock
*/

+static u64 cpu_clock_count(struct perf_event *event)
+{
+ u64 now = local_clock();
+
+ if (event->attr.exclude_idle)
+ now -= idle_task(event->oncpu)->se.sum_exec_runtime;
+
+ return now;
+}
+
static void cpu_clock_event_update(struct perf_event *event)
{
- s64 prev;
+ s64 prev, delta;
u64 now;

- now = local_clock();
+ now = cpu_clock_count(event);
prev = local64_xchg(&event->hw.prev_count, now);
- local64_add(now - prev, &event->count);
+ delta = now - prev;
+ if (delta > 0)
+ local64_add(delta, &event->count);
}

static void cpu_clock_event_start(struct perf_event *event, int flags)
{
- local64_set(&event->hw.prev_count, local_clock());
+ u64 now = cpu_clock_count(event);
+
+ local64_set(&event->hw.prev_count, now);
perf_swevent_start_hrtimer(event);
}

diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
index d518664cce4f..e360ce5dd9a2 100644
--- a/kernel/sched/idle_task.c
+++ b/kernel/sched/idle_task.c
@@ -27,9 +27,14 @@ static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int fl
static struct task_struct *
pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
+ struct task_struct *idle = rq->idle;
+
put_prev_task(rq, prev);
update_idle_core(rq);
schedstat_inc(rq->sched_goidle);
+
+ idle->se.exec_start = rq_clock_task(rq);
+
return rq->idle;
}

@@ -48,6 +53,15 @@ dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)

static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
{
+ struct task_struct *idle = rq->idle;
+ u64 delta, now;
+
+ now = rq_clock_task(rq);
+ delta = now - idle->se.exec_start;
+ if (likely((s64)delta > 0))
+ idle->se.sum_exec_runtime += delta;
+ idle->se.exec_start = now;
+
rq_last_tick_reset(rq);
}

@@ -57,6 +71,9 @@ static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)

static void set_curr_task_idle(struct rq *rq)
{
+ struct task_struct *idle = rq->idle;
+
+ idle->se.exec_start = rq_clock_task(rq);
}

static void switched_to_idle(struct rq *rq, struct task_struct *p)
--
2.13.6
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