linux-kernel - Re: [PATCH 4/4] cpufreq: intel_pstate: enable boost for Skylake Xeon

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Date:   Sat, 28 Jul 2018 07:14:24 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Francisco Jerez <currojerez@...eup.net>, lenb@...nel.org,
        rjw@...ysocki.net, mgorman@...hsingularity.net
Cc:     peterz@...radead.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        viresh.kumar@...aro.org, ggherdovich@...e.cz,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Eero Tamminen <eero.t.tamminen@...el.com>
Subject: Re: [PATCH 4/4] cpufreq: intel_pstate: enable boost for Skylake Xeon

On Fri, 2018-07-27 at 22:34 -0700, Francisco Jerez wrote:
> Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com> writes:
> 
> > Enable HWP boost on Skylake server and workstations.
> > 
> 
> Please revert this series, it led to significant energy usage and
> graphics performance regressions [1]. 
Which SKX platform is targeted to graphics?

>  The reasons are roughly the ones
> we discussed by e-mail off-list last April: This causes the
> intel_pstate
> driver to decrease the EPP to zero 
No. You didn't check this series. We are not using EPP at all.
The boost mechanism used here is not boost to max.

Thanks,
Srinivas

> when the workload blocks on IO
> frequently enough, which for the regressing benchmarks detailed in
> [1]
> is a symptom of the workload being heavily IO-bound, which means they
> won't benefit at all from the EPP boost since they aren't
> significantly
> CPU-bound, and they will suffer a decrease in parallelism due to the
> active CPU core using a larger fraction of the TDP in order to
> achieve
> the same work, causing the GPU to have a lower power budget
> available,
> leading to a decrease in system performance.
> 
> You may want to give a shot to my previous suggestion of using [2] in
> order to detect whether the system is IO-bound, which you can use as
> an
> indicator that the optimization implemented in this series cannot
> possibly improve performance and can be expected to hurt energy
> usage.
> 
> Thanks.
> 
> [1] https://bugs.freedesktop.org/show_bug.cgi?id=107410
> [2] https://patchwork.kernel.org/patch/10312259/
> 
> > Reported-by: Mel Gorman <mgorman@...hsingularity.net>
> > Tested-by: Giovanni Gherdovich <ggherdovich@...e.cz>
> > Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel
> > .com>
> > ---
> >  drivers/cpufreq/intel_pstate.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/cpufreq/intel_pstate.c
> > b/drivers/cpufreq/intel_pstate.c
> > index 70bf63bb4e0e..01c8da1f99db 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -1794,6 +1794,12 @@ static const struct x86_cpu_id
> > intel_pstate_cpu_ee_disable_ids[] = {
> >  	{}
> >  };
> >  
> > +static const struct x86_cpu_id intel_pstate_hwp_boost_ids[]
> > __initconst = {
> > +	ICPU(INTEL_FAM6_SKYLAKE_X, core_funcs),
> > +	ICPU(INTEL_FAM6_SKYLAKE_DESKTOP, core_funcs),
> > +	{}
> > +};
> > +
> >  static int intel_pstate_init_cpu(unsigned int cpunum)
> >  {
> >  	struct cpudata *cpu;
> > @@ -1824,6 +1830,10 @@ static int intel_pstate_init_cpu(unsigned
> > int cpunum)
> >  			intel_pstate_disable_ee(cpunum);
> >  
> >  		intel_pstate_hwp_enable(cpu);
> > +
> > +		id = x86_match_cpu(intel_pstate_hwp_boost_ids);
> > +		if (id)
> > +			hwp_boost = true;
> >  	}
> >  
> >  	intel_pstate_get_cpu_pstates(cpu);
> > -- 
> > 2.13.6