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

[Greg Kroah-Hartman]

On Wed, Mar 16, 2016 at 05:00:07PM -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_bug.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@xxxxxxxxx>
> >>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@xxxxxxxxxxxx>
> >>     Tested-by: szegad <szegadlo@xxxxxxxxxxxxxx>
> >>     Tested-by: prash <prash.n.rao@xxxxxxxxx>
> >>     Tested-by: amish <ammdispose-arch@xxxxxxxxx>
> >>     Tested-by: Matthias <morpheusxyz123@xxxxxxxx>
> >>     Reviewed-by: Javi Merino <javi.merino@xxxxxxx>
> >>     Signed-off-by: Zhang Rui <rui.zhang@xxxxxxxxx>
> >>     Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> >>     Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >>
> >>
> >>
> >>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.

Great, we are "bug compatible" :)

Can you please work to get this resolved in Linus's tree and then we can
backport the needed changes into the 4.4-stable release.

Zhang, any ideas here?

thanks,

greg k-h