linux-kernel - Re: [PATCH v2 1/2] cpufreq: Make iowait boost a policy option

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Message-ID: <20170519094245.ztm6tt2iwkaiwsya@hirez.programming.kicks-ass.net>
Date:   Fri, 19 May 2017 11:42:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2 1/2] cpufreq: Make iowait boost a policy option

On Thu, May 18, 2017 at 11:23:43PM -0700, Joel Fernandes wrote:
> Make iowait boost a cpufreq policy option and enable it for intel_pstate
> cpufreq driver. Governors like schedutil can use it to determine if
> boosting for tasks that wake up with p->in_iowait set is needed.

Rather than just flat out disabling the option, is there something
better we can do on ARM?

The reason for the IO-wait boost is to ensure we feed our external
devices data ASAP, this reduces wait times, increases throughput and
decreases the duration the devices have to operate.

I realize max freq/volt might not be the best option for you, but is
there another spot that would make sense? I can imagine you want to
return your MMC to low power state ASAP as well.

So rather than a disable flag, I would really rather see an IO-wait OPP
state selector or something.