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

[Laura Abbott]

(bringing this back to the main thread)

On 03/16/2016 05:20 PM, Pandruvada, Srinivas wrote:
> 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@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@xxxxxxxxxxxxxxxxxx
> > > > 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

A separate thread was started which gave this insight:

"I think
the problem is your device has a passive trip temp of 0
/sys/class/thermal/thermal_zone0/trip_point_2_temp:0
/sys/class/thermal/thermal_zone0/trip_point_2_type:passive

Which triggers a false throttle = true. I think we should this trip as
invalid in the case of
if (tz->temperature >= trip_temp) {} check
in thermal_zone_trip_update()."

So would something like the following work?

diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
index ea9366a..1228797 100644
--- a/drivers/thermal/step_wise.c
+++ b/drivers/thermal/step_wise.c
@@ -143,7 +143,7 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 
        trend = get_tz_trend(tz, trip);
 
-       if (tz->temperature >= trip_temp) {
+       if (trip_type != THERMAL_TRIPS_NONE && tz->temperature >= trip_temp) {
                throttle = true;
                trace_thermal_zone_trip(tz, trip, trip_type);
        }

(completely untested, no idea if I'm even close)

Thanks,
Laura