linux-kernel - Re: Default governor regardless of cpuidle driver

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Message-ID: <b759d5a9-f418-817e-eefa-2302d17cb6ea@linaro.org>
Date:   Thu, 29 Aug 2019 23:51:46 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Joao Martins <joao.m.martins@...cle.com>
Cc:     Marcelo Tosatti <mtosatti@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, linux-pm@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: Default governor regardless of cpuidle driver

On 29/08/2019 23:12, Joao Martins wrote:

[ ... ]

>>> Say you wanted to have a kvm specific config, you would still see the same
>>> problem if you happen to compile intel_idle together with haltpoll
>>> driver+governor. 
>>
>> Can a guest work with an intel_idle driver?
>>
> Yes.
> 
> If you use Qemu you would add '-overcommit cpu-pm=on' to try it out. ofc,
> assuming you're on a relatively recent Qemu (v3.0+) and a fairly recent kernel
> version as host (v4.17+).

Ok, thanks for the clarification.

>>> Creating two separate configs here, with and without haltpoll
>>> for VMs doesn't sound effective for distros.
>>
>> Agree
>>
>>> Perhaps decreasing the rating of
>>> haltpoll governor, but while a short term fix it wouldn't give much sensible
>>> defaults without the one-off runtime switch.

The rating has little meaning because each governor fits a specific
situation (server, desktop, etc...) and it would probably make sense to
remove it and add a default governor in the config file like the cpufreq.

May be I missed the point from some previous discussion but IMHO the
problem you are facing is coming from the design: there is no need to
create a halt governor but move the code inside the cpuidle-halt driver
instead and ignore the state asked by the governor and return the state
the driver entered.



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