linux-kernel - Re: [PATCH 1/1] intel_pstate: Increase hold-off time before busyness is scaled

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Date:	Thu, 18 Feb 2016 23:29:51 +0000
From:	"Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
To:	"mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
	"rafael@...nel.org" <rafael@...nel.org>
CC:	"matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"Brandewie, Dirk J" <dirk.j.brandewie@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"umgwanakikbuti@...il.com" <umgwanakikbuti@...il.com>
Subject: Re: [PATCH 1/1] intel_pstate: Increase hold-off time before
 busyness is scaled

On Thu, 2016-02-18 at 20:43 +0100, Rafael J. Wysocki wrote:
> Hi Mel,
> 
> On Thu, Feb 18, 2016 at 12:11 PM, Mel Gorman
> <mgorman@...hsingularity.net> wrote:
> 
> [cut]
> 
> > 
> > Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> > ---
> >  drivers/cpufreq/intel_pstate.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/cpufreq/intel_pstate.c
> > b/drivers/cpufreq/intel_pstate.c
> > index cd83d477e32d..54250084174a 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -999,7 +999,7 @@ static inline int32_t
> > get_target_pstate_use_performance(struct cpudata *cpu)
> >         sample_time = pid_params.sample_rate_ms  * USEC_PER_MSEC;
> >         duration_us = ktime_us_delta(cpu->sample.time,
> >                                      cpu->last_sample_time);
> > -       if (duration_us > sample_time * 3) {
> > +       if (duration_us > sample_time * 12) {
> >                 sample_ratio = div_fp(int_tofp(sample_time),
> >                                       int_tofp(duration_us));
> >                 core_busy = mul_fp(core_busy, sample_ratio);
> > --
> 
> I've been considering making a change like this, but I wasn't quite
> sure how much greater the multiplier should be, so I've queued this
> one up for 4.6.
> 
We need to test power impact on different server workloads. So please
hold on.
We have server folks complaining that we already consume too much
power.

Thanks,
Srinivas

> That said please note that we're planning to make one significant
> change to intel_pstate in the 4.6 cycle that's very likely to affect
> your results.
> 
> It is currently present in linux-next (commit 402c43ed2d74 "cpufreq:
> intel_pstate: Replace timers with utilization update callbacks" in
> the
> linux-next branch of the linux-pm.git tree, that depends on commit
> fe7034338ba0 "cpufreq: Add mechanism for registering utilization
> update callbacks" in the same branch).  Also you can just pull from
> the pm-cpufreq-test branch in linux-pm.git, but that contains much
> more material.
> 
> Thanks,
> Rafael
> --
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