linux-kernel - Re: [PATCH 1/9] perf: Remove redundant parent context check from context

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Date:	Tue, 9 Sep 2014 12:20:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Jen-Cheng(Tommy) Huang" <tommy24@...ech.edu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/9] perf: Remove redundant parent context check from
 context_equiv

On Mon, Sep 08, 2014 at 06:45:24PM +0200, Jiri Olsa wrote:
> I just noticed that we initialize the child state with base parent
> state not the real (immediate) parent.. which is what we want IMO
> 
> I wonder attached patch could fix the issue mentioned in:
>   1f9a726 perf: Do not allow optimized switch for non-cloned events
> 
> now I need to recall what I used to test this ;-)

Ah, very nice! Yes this might just do it.

> ---
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index e4d6924..561a4ea 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7794,6 +7794,7 @@ inherit_event(struct perf_event *parent_event,
>  	      struct perf_event *group_leader,
>  	      struct perf_event_context *child_ctx)
>  {
> +	enum perf_event_active_state parent_state = parent_event->state;
>  	struct perf_event *child_event;
>  	unsigned long flags;
>  
> @@ -7827,7 +7828,7 @@ inherit_event(struct perf_event *parent_event,
>  	 * not its attr.disabled bit.  We hold the parent's mutex,
>  	 * so we won't race with perf_event_{en, dis}able_family.
>  	 */
> -	if (parent_event->state >= PERF_EVENT_STATE_INACTIVE)
> +	if (parent_state >= PERF_EVENT_STATE_INACTIVE)
>  		child_event->state = PERF_EVENT_STATE_INACTIVE;
>  	else
>  		child_event->state = PERF_EVENT_STATE_OFF;

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