linux-kernel - Re: [PATCH v9 5/5] arm64: Update AMU-based freq scale factor on entering idle

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Message-ID: <fe4c48e0-5bc5-4a16-8df2-e848b55c1015@linux.microsoft.com>
Date: Fri, 24 Jan 2025 10:15:11 +0530
From: Prasanna Kumar T S M <ptsm@...ux.microsoft.com>
To: Beata Michalska <beata.michalska@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
 ionela.voinescu@....com, sudeep.holla@....com, will@...nel.org,
 catalin.marinas@....com, rafael@...nel.org, viresh.kumar@...aro.org
Cc: sumitg@...dia.com, yang@...amperecomputing.com,
 vanshikonda@...amperecomputing.com, lihuisong@...wei.com,
 zhanjie9@...ilicon.com
Subject: Re: [PATCH v9 5/5] arm64: Update AMU-based freq scale factor on
 entering idle


On 21-01-2025 14:14, Beata Michalska wrote:
> Now that the frequency scale factor has been activated for retrieving
> current frequency on a given CPU, trigger its update upon entering
> idle. This will, to an extent, allow querying last known frequency
> in a non-invasive way. It will also improve the frequency scale factor
> accuracy when a CPU entering idle did not receive a tick for a while.
> As a consequence, for idle cores, the reported frequency will be the
> last one observed before entering the idle state.
>
> Suggested-by: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
> Signed-off-by: Beata Michalska <beata.michalska@....com>
> ---
>   arch/arm64/kernel/topology.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
>
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 5f5738b174c7..6c43aafac77c 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -213,6 +213,19 @@ static __always_inline bool amu_fie_cpu_supported(unsigned int cpu)
>   		cpumask_test_cpu(cpu, amu_fie_cpus);
>   }
>   
> +void arch_cpu_idle_enter(void)
> +{
> +	unsigned int cpu = smp_processor_id();
> +
> +	if (!amu_fie_cpu_supported(cpu))
> +		return;
> +
> +	/* Kick in AMU update but only if one has not happened already */
> +	if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
> +	    time_is_before_jiffies(per_cpu(cpu_amu_samples.last_scale_update, cpu)))
> +		amu_scale_freq_tick();
> +}
> +
>   #define AMU_SAMPLE_EXP_MS	20
>   
>   int arch_freq_get_on_cpu(int cpu)

Looks good to me.

Reviewed-by: Prasanna Kumar T S M <ptsm@...ux.microsoft.com>