linux-kernel - Re: [PATCH V3] SKL intel_pstate update MSR values when changing governors

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Date:	Tue, 24 Nov 2015 17:36:59 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Alexandra Yates <alexandra.yates@...ux.intel.com>,
	Len Brown <lenb@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3] SKL intel_pstate update MSR values when changing governors

On Tuesday, November 24, 2015 07:57:42 AM Srinivas Pandruvada wrote:
> On Tue, 2015-11-24 at 15:28 +0100, Rafael J. Wysocki wrote:
> > On Monday, November 23, 2015 05:17:36 PM Srinivas Pandruvada wrote:
> > > On Tue, 2015-11-24 at 02:09 +0100, Rafael J. Wysocki wrote:
> > > > Hi,
> > > > 
> > > > On Sat, Nov 21, 2015 at 1:16 AM, Srinivas Pandruvada
> > > > <srinivas.pandruvada@...ux.intel.com> wrote:
> > > > > 
> > 
> > [cut]
> > 
> > > > 
> > > > > > For more information on the MSR values for SKL please visit
> > > > > > ISDM under Managing HWP.
> > > > > > 
> > > > > > Signed-off-by: Alexandra Yates <
> > > > > > alexandra.yates@...ux.intel.com>
> > > > > 
> > > > > Acked-by: Srinivas Pandruvada <
> > > > > srinivas.pandruvada@...ux.intel.com>
> > > > > > 
> > > > > > ---
> > > > > >   drivers/cpufreq/intel_pstate.c | 2 ++
> > > > > >   1 file changed, 2 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/cpufreq/intel_pstate.c
> > > > > > b/drivers/cpufreq/intel_pstate.c
> > > > > > index 2e31d09..0eeb7da 100644
> > > > > > --- a/drivers/cpufreq/intel_pstate.c
> > > > > > +++ b/drivers/cpufreq/intel_pstate.c
> > > > > > @@ -1242,6 +1242,8 @@ static int
> > > > > > intel_pstate_set_policy(struct
> > > > > > cpufreq_policy *policy)
> > > > > >             policy->max >= policy->cpuinfo.max_freq) {
> > > > > >                 pr_debug("intel_pstate: set performance\n");
> > > > > >                 limits = &performance_limits;
> > > > > > +               if (hwp_active)
> > > > > > +                       intel_pstate_hwp_set();
> > > > 
> > > > Honestly, I'm not really sure how this is matching the changelog.
> > > > 
> > > > What it does is to ensure that the correct limits are used when
> > > > in the
> > > > HWP mode too as far as I can say.  Is my understanding correct
> > > > here?
> > > Yes.
> > 
> > OK
> > 
> > But if we make the "performance" limits take effect here, it will
> > effectively
> > make HWP use min = max = 100%, right?  Is that what we want to happen
> > here?
> Yes. intel_pstate_hwp_set() uses limits->min_perf_pct and limits
> ->max_perf_pct to set HWP limits. Here these will be set to 100%.

OK, so that's the intended behavior of "performance" in the HWP case, right?

I'll apply this patch, but I'm going to write a new changelog for it, then.

Thanks,
Rafael

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