linux-kernel - Re: [PATCH] perf: arm_spe: Relax period restriction

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Message-ID: <20250527130650.GH2566836@e132581.arm.com>
Date: Tue, 27 May 2025 14:06:50 +0100
From: Leo Yan <leo.yan@....com>
To: Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: arm_spe: Relax period restriction

Hi all,

On Tue, May 27, 2025 at 01:18:27PM +0100, Leo Yan wrote:

[...]

> @@ -309,15 +309,22 @@ static u64 arm_spe_event_to_pmscr(struct perf_event *event)
>  static void arm_spe_event_sanitise_period(struct perf_event *event)
>  {
>  	struct arm_spe_pmu *spe_pmu = to_spe_pmu(event->pmu);
> +	struct device *dev = &spe_pmu->pdev->dev;
>  	u64 period = event->hw.sample_period;
>  	u64 max_period = PMSIRR_EL1_INTERVAL_MASK;
>  
> -	if (period < spe_pmu->min_period)
> -		period = spe_pmu->min_period;
> -	else if (period > max_period)
> +	if (period < spe_pmu->min_period) {
> +		/* Period must set to a non-zero value */
> +		if (!period)
> +			period = 1;

I read the document again and found the interval granluarity is 256
(8-bit).  So the change above is incorrect.

I will send a new patch.  Sorry for inconvenience.

Thanks,
Leo

> +
> +		dev_warn_ratelimited(dev, "Period %llu < %u (recommended minimum interval).\n",
> +				     period, spe_pmu->min_period);
> +	} else if (period > max_period) {
>  		period = max_period;
> -	else
> +	} else {
>  		period &= max_period;
> +	}
>  
>  	event->hw.sample_period = period;
>  }
> -- 
> 2.34.1
>