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

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Date:   Fri, 19 May 2017 12:21:16 +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>,
        Juri Lelli <juri.lelli@...il.com>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH v2 1/2] cpufreq: Make iowait boost a policy option

On Fri, May 19, 2017 at 11:42:45AM +0200, Peter Zijlstra wrote:
> 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.

It would be even better if we can determine that point from the power
model data.