linux-kernel - Re: [PATCH] perf, x86: Allow setting period 1

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Message-ID: <m238vfil5j.fsf@firstfloor.org>
Date:	Thu, 28 Mar 2013 08:44:40 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	a.p.zijlstra@...llo.nl
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] perf, x86: Allow setting period 1

Andi Kleen <andi@...stfloor.org> writes:

> From: Andi Kleen <ak@...ux.intel.com>
>
> I had some requests for setting period 1, so that every event of something
> is caught.  To my knowledge there is no limit to 1 on Intel hardware.
> Just remove the check for minimum 2

Ping! patch is missing review.

>
> If specific CPUs have problems we can black list them.
>
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/perf_event.c |    5 -----
>  1 files changed, 0 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index bf0f01a..2b394ae 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -946,11 +946,6 @@ int x86_perf_event_set_period(struct perf_event *event)
>  		hwc->last_period = period;
>  		ret = 1;
>  	}
> -	/*
> -	 * Quirk: certain CPUs dont like it if just 1 hw_event is left:
> -	 */
> -	if (unlikely(left < 2))
> -		left = 2;
>  
>  	if (left > x86_pmu.max_period)
>  		left = x86_pmu.max_period;

-- 
ak@...ux.intel.com -- Speaking for myself only
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