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List: linux-pm
Subject: Re: [PATCH] cpufreq: Honour transition_latency over transition_delay_us
From: "Rafael J. Wysocki" <rafael () kernel ! org>
Date: 2024-02-29 19:26:01
Message-ID: CAJZ5v0hdZc2Usfa8m_DrVr6ZnzqZOUd60grGySz-EkyMgtzNjA () mail ! gmail ! com
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On Wed, Feb 28, 2024 at 12:35 AM Qais Yousef <qyousef@layalina.io> wrote:
>
> Some platforms like Arm's Juno can have a high transition latency that
> can be larger than the 2ms cap introduced. If a driver report
> a transition_latency that is higher than the cap, then use it as-is.
>
> Update comment s/10/2/ to reflect the new cap of 2ms.
>
> Reported-by: Pierre Gondois <pierre.gondois@arm.com>
> Signed-off-by: Qais Yousef <qyousef@layalina.io>
> ---
> drivers/cpufreq/cpufreq.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 66cef33c4ec7..926a51cb7e52 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -576,8 +576,17 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy)
>
> latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
> if (latency) {
> + unsigned int max_delay_us = 2 * MSEC_PER_SEC;
> +
> + /*
> + * If the platform already has high transition_latency, use it
> + * as-is.
> + */
> + if (latency > max_delay_us)
> + return latency;
> +
> /*
> - * For platforms that can change the frequency very fast (< 10
> + * For platforms that can change the frequency very fast (< 2
> * us), the above formula gives a decent transition delay. But
> * for platforms where transition_latency is in milliseconds, it
> * ends up giving unrealistic values.
> @@ -586,7 +595,7 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy)
> * a reasonable amount of time after which we should reevaluate
> * the frequency.
> */
> - return min(latency * LATENCY_MULTIPLIER, (unsigned int)(2 * MSEC_PER_SEC));
> + return min(latency * LATENCY_MULTIPLIER, max_delay_us);
> }
>
> return LATENCY_MULTIPLIER;
> --
Applied as 6.9 material, thanks!
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