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Date:	Wed, 07 Oct 2015 01:06:17 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq, intel_pstate, set max_sysfs_pct and min_sysfs_pct on governor switch

On Wednesday, October 07, 2015 12:43:55 AM Rafael J. Wysocki wrote:
> On Tuesday, October 06, 2015 05:49:07 PM Prarit Bhargava wrote:
> > Intel CPUs will not enter higher p-states when after switching from the
> > performance governor to the powersave governor, until
> > /sys/devices/system/cpu/intel_pstate/min_perf_pct is set to a low value.
> > This differs from previous behaviour in which a switch to the powersave
> > governor would result in a low default value for min_perf_pct.
> > 
> > The behavior of the powersave governor changed after commit a04759924e25
> > ("[cpufreq] intel_pstate: honor user space min_perf_pct override on
> > resume").  The commit introduced tracking of performance percentage
> > changes via sysfs in order to restore userspace changes during
> > suspend/resume.  The problem occurs because the global values of the newly
> > introduced max_sysfs_pct and min_sysfs_pct are not reset on a governor
> > change and this causes the new governor to inherit the previous governor's
> > settings.
> > 
> > This patch sets max_sysfs_pct to 100 and min_sysfs_pct to 0 on a governor
> > change which fixes the problem with governor switching.  These changes
> > also make the initial calculations for max_perf_pct and min_perf_pct
> > slightly simpler.
> > 
> > Before patch:
> > [root@...el-skylake-y-01 power]# cpupower frequency-set -g performance
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
> > 100
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
> > 100
> > [root@...el-skylake-y-01 power]# cpupower frequency-set -g powersave
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
> > 100
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
> > 100
> > 
> > After patch:
> > [root@...el-skylake-y-01 power]# cpupower frequency-set -g performance
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
> > 100
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
> > 100
> > [root@...el-skylake-y-01 power]# cpupower frequency-set -g powersave
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
> > 14
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
> > 100
> > 
> > Also note that I have tested suspend/resume (using CONFIG_PM_DEBUG):
> > [root@...el-skylake-y-01 power]# echo 50 > /sys/devices/system/cpu/intel_pstate/min_perf_pct
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/*_perf_pct
> > 100
> > 50
> > [root@...el-skylake-y-01 power]# echo devices > /sys/power/pm_test
> > [root@...el-skylake-y-01 power]# echo platform > /sys/power/disk
> > [root@...el-skylake-y-01 power]# echo disk > /sys/power/state
> > [root@...el-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/*_perf_pct
> > 100
> > 50
> > 
> > Fixes: a04759924e25 ("[cpufreq] intel_pstate: honor user space min_perf_pct override on resume")
> > Cc: Kristen Carlson Accardi <kristen@...ux.intel.com>
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > Cc: Viresh Kumar <viresh.kumar@...aro.org>
> > Cc: linux-pm@...r.kernel.org
> > Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> > ---
> >  drivers/cpufreq/intel_pstate.c |    7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > index 3af9dd7..bb24458 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -986,6 +986,9 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
> >  	if (!policy->cpuinfo.max_freq)
> >  		return -ENODEV;
> >  
> > +	limits.min_sysfs_pct = 0;
> > +	limits.max_sysfs_pct = 100;
> > +
> >  	if (policy->policy == CPUFREQ_POLICY_PERFORMANCE &&
> >  	    policy->max >= policy->cpuinfo.max_freq) {
> >  		limits.min_policy_pct = 100;
> > @@ -1004,9 +1007,9 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
> >  	limits.max_policy_pct = clamp_t(int, limits.max_policy_pct, 0 , 100);
> >  
> >  	/* Normalize user input to [min_policy_pct, max_policy_pct] */
> > -	limits.min_perf_pct = max(limits.min_policy_pct, limits.min_sysfs_pct);
> > +	limits.min_perf_pct = limits.min_policy_pct;
> >  	limits.min_perf_pct = min(limits.max_policy_pct, limits.min_perf_pct);
> > -	limits.max_perf_pct = min(limits.max_policy_pct, limits.max_sysfs_pct);
> > +	limits.max_perf_pct = limits.max_sysfs_pct;

On a second thought, isn't that always 100?  If so, doesn't it basically discard
limits.max_policy_pct?

> >  	limits.max_perf_pct = max(limits.min_policy_pct, limits.max_perf_pct);
> >  
> >  	/* Make sure min_perf_pct <= max_perf_pct */
> > 

Thanks,
Rafael

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