Re: [REGRESSION] 774ac8b7eff6 ("Thermal: initialize thermal zone device correctly") causes performance drop

["Pandruvada, Srinivas" <srinivas.pandruvada@intel.com>]

On Wed, 2016-03-16 at 17:00 -0700, Laura Abbott wrote:
> On 03/16/2016 03:46 PM, Greg Kroah-Hartman wrote:
> > On Wed, Mar 16, 2016 at 03:27:57PM -0700, Laura Abbott wrote:
> > > Hi,
> > > 
> > > Fedora received a bug report (https://bugzilla.redhat.com/show_bu
> > > g.cgi?id=1317190)
> > > of a major performance drop on various bench marks and general
> > > system
> > > sluggishness with the 4.4.4 kernel update. The benchmarks were
> > > showing
> > > a reduction to about 18% performance (not minor).
> > > 
> > > Bisection showed the first bad commit was
> > > 
> > > commit 774ac8b7eff69e0786970157de2157e68b22f456
> > > Author: Zhang Rui <rui.zhang@intel.com>
> > > Date:   Fri Oct 30 16:31:47 2015 +0800
> > > 
> > >      Thermal: initialize thermal zone device correctly
> > >      commit bb431ba26c5cd0a17c941ca6c3a195a3a6d5d461 upstream.
> > >      After thermal zone device registered, as we have not read
> > > any
> > >      temperature before, thus tz->temperature should not be 0,
> > >      which actually means 0C, and thermal trend is not available.
> > >      In this case, we need specially handling for the first
> > >      thermal_zone_device_update().
> > >      Both thermal core framework and step_wise governor is
> > >      enhanced to handle this. And since the step_wise governor
> > >      is the only one that uses trends, so it's the only thermal
> > >      governor that needs to be updated.
> > >      Tested-by: Manuel Krause <manuelkrause@netscape.net>
> > >      Tested-by: szegad <szegadlo@poczta.onet.pl>
> > >      Tested-by: prash <prash.n.rao@gmail.com>
> > >      Tested-by: amish <ammdispose-arch@yahoo.com>
> > >      Tested-by: Matthias <morpheusxyz123@yahoo.de>
> > >      Reviewed-by: Javi Merino <javi.merino@arm.com>
> > >      Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> > >      Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> > >      Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.or
> > > g>
> > > 
> > > 
> > > 
> > > Reverting this plus to other commits in the series (a67208e94d94
> > > "Thermal: handle thermal zone device properly during system
> > > sleep"
> > > and 27f356149d59 "Thermal: do thermal zone update after a cooling
> > > device registered") confirmed the performance was back to normal.
> > > 
> > > Bugzilla has the full discussion but this comment from one of the
> > > reporters sums it up:
> > > 
> > > "In 4.4.3 and prior, my 2.40 MHz processor would fluctuate
> > > between
> > > 1000 and 3400 MHz.  In 4.4.4, the processor would fluctuate
> > > between
> > > 400 and 700 MHz, according to /proc/cpuinfo.
> > > 
> > > Setting /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
> > > to
> > > performance, instead of the default "powersave" forces the CPU to
> > > 2400 MHz, and improves performance greatly, but still not to the
> > > same level as in 4.4.3."
> > > 
> > > Any ideas?
> > 
> > Is this same "slowdown" also seen in 4.5?
> > 
> > thanks,
> > 
> > greg k-h
> > 
> 
> Yes, the same issue is seen on 4.5 according to the reporter.
What does it show here when performance drops?
grep . /sys/devices/system/cpu/intel_pstate/*

Is the problem still occurs if you set 
/sys/class/thermal/thermal_zone*/mode to "disabled" 

Thanks,
Srinivas

> 
> Thanks,
> Laura
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