linux-kernel - Re: [PATCH 2/2] arm: disable frequency invariance for CONFIG_BL

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Date:   Tue, 6 Oct 2020 12:40:34 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ionela Voinescu <ionela.voinescu@....com>
Cc:     catalin.marinas@....com, sudeep.holla@....com, will@...nel.org,
        linux@...linux.org.uk, rjw@...ysocki.net, dietmar.eggemann@....com,
        valentin.schneider@....com, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm: disable frequency invariance for
 CONFIG_BL_SWITCHER

On 24-09-20, 13:30, Ionela Voinescu wrote:
> big.LITTLE switching complicates the setting of a correct cpufreq-based
> frequency invariance scale factor due to (as observed in
> drivers/cpufreq/vexpress-spc-cpufreq.c):
>  - Incorrect current and maximum frequencies as a result of the
>    exposure of a virtual frequency table to the cpufreq core,
>  - Missed updates as a result of asynchronous frequency adjustments
>    caused by frequency changes in other CPU pairs.
> 
> Given that its functionality is atypical in regards to frequency
> invariance and this is an old technology, disable frequency
> invariance for when big.LITTLE switching is configured in to prevent
> incorrect scale setting.
> 
> Signed-off-by: Ionela Voinescu <ionela.voinescu@....com>
> Suggested-by: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Russell King <linux@...linux.org.uk>
> Cc: Catalin Marinas <catalin.marinas@....com>
> ---
>  arch/arm/include/asm/topology.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
> index e5e3d5ce4d55..470299ee2fba 100644
> --- a/arch/arm/include/asm/topology.h
> +++ b/arch/arm/include/asm/topology.h
> @@ -7,10 +7,13 @@
>  #include <linux/cpumask.h>
>  #include <linux/arch_topology.h>
>  
> +/* big.LITTLE switcher is incompatible with frequency invariance */
> +#ifndef CONFIG_BL_SWITCHER
>  /* Replace task scheduler's default frequency-invariant accounting */
>  #define arch_set_freq_scale topology_set_freq_scale
>  #define arch_scale_freq_capacity topology_get_freq_scale
>  #define arch_scale_freq_invariant topology_scale_freq_invariant
> +#endif
>  
>  /* Replace task scheduler's default cpu-invariant accounting */
>  #define arch_scale_cpu_capacity topology_get_cpu_scale

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh