linux-kernel - Re: [PATCH v6 2/2] sched/topology: change behaviour of sysctl sched_energy

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Message-ID: <xhsmhmswronoo.mognet@vschneid.remote.csb>
Date:   Mon, 09 Oct 2023 16:49:59 +0200
From:   Valentin Schneider <vschneid@...hat.com>
To:     Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>, mingo@...hat.com,
        peterz@...radead.org, vincent.guittot@...aro.org
Cc:     sshegde@...ux.vnet.ibm.com, dietmar.eggemann@....com,
        linux-kernel@...r.kernel.org, qperret@...gle.com,
        srikar@...ux.vnet.ibm.com, mingo@...nel.org,
        pierre.gondois@....com, yu.c.chen@...el.com,
        tim.c.chen@...ux.intel.com, pauld@...hat.com, lukasz.luba@....com,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 2/2] sched/topology: change behaviour of sysctl
 sched_energy_aware based on the platform

On 09/10/23 11:30, Shrikanth Hegde wrote:
> sysctl sched_energy_aware is available for the admin to disable/enable
> energy aware scheduling(EAS). EAS is enabled only if few conditions are
> met by the platform. They are, asymmetric CPU capacity, no SMT,
> schedutil CPUfreq governor, frequency invariant load tracking etc.
> A platform may boot without EAS capability, but could gain such
> capability at runtime. For example, changing/registering the CPUfreq
> governor to schedutil.
>
> At present, though platform doesn't support EAS, this sysctl returns 1
> and it ends up calling build_perf_domains on write to 1 and
> NOP when writing to 0. That is confusing and un-necessary.
>
> Desired behavior would be to have this sysctl to enable/disable the EAS
> on supported platform. On non-supported platform write to the sysctl
> would return not supported error and read of the sysctl would return
> empty. So
> sched_energy_aware returns empty - EAS is not possible at this moment
> This will include EAS capable platforms which have at least one EAS
> condition false during startup, e.g. not using the schedutil CPUfreq governor
> sched_energy_aware returns 0 - EAS is supported but disabled by admin.
> sched_energy_aware returns 1 - EAS is supported and enabled.
>
> User can find out the reason why EAS is not possible by checking
> info messages. sched_is_eas_possible returns true if the platform
> can do EAS at this moment.
>
> Tested-by: Pierre Gondois <pierre.gondois@....com>
> Signed-off-by: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>

Reviewed-by: Valentin Schneider <vschneid@...hat.com>