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

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Message-ID: <391cd0ea-3eec-44ae-a297-9e2d69000e95@nvidia.com>
Date: Wed, 29 Jan 2025 16:43:19 +0530
From: Sumit Gupta <sumitg@...dia.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: <yang@...amperecomputing.com>, <vanshikonda@...amperecomputing.com>,
	<lihuisong@...wei.com>, <zhanjie9@...ilicon.com>, linux-tegra
	<linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v9 5/5] arm64: Update AMU-based freq scale factor on
 entering idle



On 21/01/25 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>

Reviewed-by: Sumit Gupta <sumitg@...dia.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)
> --
> 2.25.1
>