linux-kernel - Re: [PATCH 3/3] perf: clarify comment regarding perf_pmu

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Date:	Fri, 10 Jan 2014 10:37:48 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] perf: clarify comment regarding perf_pmu_contexts

On Thu, Jan 09, 2014 at 03:51:32PM -0800, Cody P Schafer wrote:
> Again, note that the behavior of task_ctx_nr < 0 is an exception.
> 
> Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
> ---
>  kernel/events/core.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index e9f60d0..159ef12 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6276,8 +6276,9 @@ static int perf_event_idx_default(struct perf_event *event)
>  }
>  
>  /*
> - * Ensures all contexts with the same task_ctx_nr have the same
> - * pmu_cpu_context too.
> + * Ensures all contexts with the same task_ctx_nr (where that task_ctx_nr
> + * is >=0) have the same pmu_cpu_context too. Contexts with with negative (<0)
> + * task_ctx_nr do not share pmu_cpu_contexts.
>   */

Please stay within the enum name space; the <0 really is an
implementation detail, mostly done because testing for sign is often
cheaper than an immediate comparison.
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