linux-kernel - Re: [PATCH v2 5/5] perf: Enable applicable siblings when group leader is enable-on-exec

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Date:	Wed, 23 Nov 2011 11:38:20 +0800
From:	Deng-Cheng Zhu <dczhu@...s.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	"Barzilay, Eyal" <eyal@...s.com>,
	"Fortuna, Zenon" <zenon@...s.com>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] perf: Enable applicable siblings when group leader
 is enable-on-exec

On 11/22/2011 10:23 PM, Peter Zijlstra wrote:
> On Tue, 2011-11-22 at 14:20 +0000, Zhu, DengCheng wrote:
>>> @@ -2463,11 +2461,25 @@ static int event_enable_on_exec(struct p
>>>         if (event->state>= PERF_EVENT_STATE_INACTIVE)
>>>                 return 0;
>>>
>>> -       __perf_event_mark_enabled(event, ctx);
>>> +       event->state = PERF_EVENT_STATE_INACTIVE;
>>>
>>>         return 1;
>>>   }
>>
>> By simply setting the event state in here, we bypass time stamp stuff as a result.
>> This might lead to inaccuracies...
>
> Ah, but it calls a __perf_event_mark_enabled() at the tail of
> group_enable_on_exec() which should fix that up, right?

Oh, yes. Aside from a slight piece that the __perf_event_mark_enabled()
in group_enable_on_exec() will reassign PERF_EVENT_STATE_INACTIVE to the
group leader, your patch looks good.

In fact, my another candidate for this patch is as follows (The
comment of perf_event_enable_on_exec() says "Enable all of a task's
events that have been marked enable-on-exec", so I think the added
traversal makes sense in here):

From: Deng-Cheng Zhu <dczhu@...s.com>
Date: Wed, 23 Nov 2011 11:31:18 +0800
Subject: [PATCH] perf: Enable enable-on-exec siblings

Currently, when grouped events are created disabled and enable-on-exec,
the siblings won't be enabled on exec in fact. The problem looks like:

======================================================================
-sh-4.0# perf stat -g -e r14,cycles,instructions,r12 find / >/dev/null
^Cfind: Interrupt

  Performance counter stats for 'find /':

           60684699 r14
      <not counted> cycles
      <not counted> instructions
      <not counted> r12

        4.291975113 seconds time elapsed
======================================================================

This patch fixes it.

Signed-off-by: Deng-Cheng Zhu <dczhu@...s.com>
---
  kernel/events/core.c |    6 ++++++
  1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e8457d..63527d0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2476,6 +2476,12 @@ static void perf_event_enable_on_exec(struct 
perf_event_context *ctx)
  	raw_spin_lock(&ctx->lock);
  	task_ctx_sched_out(ctx);

+	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
+		ret = event_enable_on_exec(event, ctx);
+		if (ret)
+			enabled = 1;
+	}
+
  	list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
  		ret = event_enable_on_exec(event, ctx);
  		if (ret)
--
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