linux-kernel - Re: [PATCH v7 1/2] cpufreq: schedutil: Make iowait boost more energy efficient

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Date:   Fri, 28 Jul 2017 01:54:41 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Juri Lelli <juri.lelli@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Andres Oportus <andresoportus@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v7 1/2] cpufreq: schedutil: Make iowait boost more energy efficient

On Monday, July 24, 2017 11:37:58 AM Joel Fernandes wrote:
> On Mon, Jul 24, 2017 at 1:57 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On 23-07-17, 08:54, Joel Fernandes wrote:
> >> Currently the iowait_boost feature in schedutil makes the frequency go to max
> >> on iowait wakeups.  This feature was added to handle a case that Peter
> >> described where the throughput of operations involving continuous I/O requests
> >> [1] is reduced due to running at a lower frequency, however the lower
> >> throughput itself causes utilization to be low and hence causing frequency to
> >> be low hence its "stuck".
> >>
> >> Instead of going to max, its also possible to achieve the same effect by
> >> ramping up to max if there are repeated in_iowait wakeups happening. This patch
> >> is an attempt to do that. We start from a lower frequency (policy->min)
> >> and double the boost for every consecutive iowait update until we reach the
> >> maximum iowait boost frequency (iowait_boost_max).
> >>
> >> I ran a synthetic test (continuous O_DIRECT writes in a loop) on an x86 machine
> >> with intel_pstate in passive mode using schedutil. In this test the iowait_boost
> >> value ramped from 800MHz to 4GHz in 60ms. The patch achieves the desired improved
> >> throughput as the existing behavior.
> >>
> >> [1] https://patchwork.kernel.org/patch/9735885/
> >>
> >> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> >> Cc: Len Brown <lenb@...nel.org>
> >> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> >> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> >> Cc: Ingo Molnar <mingo@...hat.com>
> >> Cc: Peter Zijlstra <peterz@...radead.org>
> >> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> >> Suggested-by: Viresh Kumar <viresh.kumar@...aro.org>
> >> Signed-off-by: Joel Fernandes <joelaf@...gle.com>
> >> ---
> >>  kernel/sched/cpufreq_schedutil.c | 38 ++++++++++++++++++++++++++++++++------
> >>  1 file changed, 32 insertions(+), 6 deletions(-)
> >
> > You Send V7 [1-2]/2 twice, Are they different ?
> 
> No they are the same. Rafael suggested reposting it with linux-pm in
> CC I just resent it.
> 
> >
> > For both the patches:
> >
> > Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> 
> Thanks!

Applied, thanks!