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 12:40:47 +0000
From:	"Zhu, DengCheng" <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



在 2011年11月23日星期三，Peter Zijlstra <a.p.zijlstra@...llo.nl> 写道：
> On Wed, 2011-11-23 at 11:38 +0800, Deng-Cheng Zhu wrote:
>
>> +     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)
>
> This isn't correct either, in this case you should then remove the other
> two iterations of pinned/flexible group lists.
>
> Also your use of list_for_each_entry_rcu() is incorrect, either you then
> should also use rcu_read_lock(), or its not needed and not use the _rcu
> list primitive at all.
>
> Now since event_list is modified under ctx->lock, and we hold that lock
> no fancy stuff is needed and we can do without.

Ah, yes you are right. Thanks. Your following patch looks good except
that event_entry should be used for ctx event_list, rather than group_entry.
Tomorrow I'll test it and get back to you.


Deng-Cheng

> ---
> Subject: perf: Fix enable_on_exec for sibling events
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Tue Nov 22 11:25:43 CET 2011
>
> Deng-Cheng Zhu reported that sibling events that were created disabled
> with enable_on_exec would never get enabled. Iterate all events instead
> of the group lists.
>
> Reported-by: Deng-Cheng Zhu <dczhu@...s.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Link: http://lkml.kernel.org/n/tip-299rxrpmmle8hp3spyxfo202@git.kernel.org
> ---
>  kernel/events/core.c |    8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
>
> Index: linux-2.6/kernel/events/core.c
> ===================================================================
> --- linux-2.6.orig/kernel/events/core.c
> +++ linux-2.6/kernel/events/core.c
> @@ -2494,13 +2494,7 @@ static void perf_event_enable_on_exec(st
>        raw_spin_lock(&ctx->lock);
>        task_ctx_sched_out(ctx);
>
> -       list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
> -               ret = event_enable_on_exec(event, ctx);
> -               if (ret)
> -                       enabled = 1;
> -       }
> -
> -       list_for_each_entry(event, &ctx->flexible_groups, group_entry) {
> +       list_for_each_entry(event, &ctx->event_list, group_entry) {
>                ret = event_enable_on_exec(event, ctx);
>                if (ret)
>                        enabled = 1;
>
> --
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