linux-kernel - Re: [PATCH v5 1/2] perf/core: Fix small negative period being ignored

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Message-ID: <20240902092053.GC4723@noisy.programming.kicks-ass.net>
Date: Mon, 2 Sep 2024 11:20:53 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Luo Gengkun <luogengkun@...weicloud.com>
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v5 1/2] perf/core: Fix small negative period being ignored

On Sat, Aug 31, 2024 at 07:43:15AM +0000, Luo Gengkun wrote:

>  kernel/events/core.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index c973e3c11e03..a9395bbfd4aa 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4092,7 +4092,11 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count, bo
>  	period = perf_calculate_period(event, nsec, count);
>  
>  	delta = (s64)(period - hwc->sample_period);
> -	delta = (delta + 7) / 8; /* low pass filter */
> +	if (delta >= 0)
> +		delta += 7;
> +	else
> +		delta -= 7;
> +	delta /= 8; /* low pass filter */
>  
>  	sample_period = hwc->sample_period + delta;
>  

OK, that makes sense, Thanks!