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

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Date:   Sat, 28 Jul 2018 22:06:28 +0000
From:   "Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
To:     "currojerez@...eup.net" <currojerez@...eup.net>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "Tamminen, Eero T" <eero.t.tamminen@...el.com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "ggherdovich@...e.cz" <ggherdovich@...e.cz>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "tvrtko.ursulin@...ux.intel.com" <tvrtko.ursulin@...ux.intel.com>,
        "chris@...is-wilson.co.uk" <chris@...is-wilson.co.uk>
Subject: Re: [PATCH 4/4] cpufreq: intel_pstate: enable boost for Skylake Xeon

On Sat, 2018-07-28 at 13:23 -0700, Francisco Jerez wrote:
> "Pandruvada, Srinivas" <srinivas.pandruvada@...el.com> writes:
> 
> > On Sat, 2018-07-28 at 07:14 -0700, Srinivas Pandruvada wrote:
> > > 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?
> > 
> > There are some Xeon E3, which is using SKL desktop CPUID.
> > Do you have a SKL desktop with FADT pm profile 
> > acpi_gbl_FADT.preferred_profile == PM_DESKTOP? You can take
> > acpidump
> > and check.
> > 
> > Also what is
> >  /sys/devices/system/cpu/intel_pstate/hwp_dynamic_boost
> > 
> 
> Eero is the one that reproduced the regressions -- Can you get
> Srinivas
> this information from your system?
I commented in the bug. Let's take there first.

Thanks,
Srinivas

> 
> Thank you.
> 
> > Thanks,
> > Srinivas
> > 
> > > 
> > > >  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
> > > > > .int
> > > > > el
> > > > > .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
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