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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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@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.org>
> 
> 
> 
> 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