Re: [LKP] [driver core] 570d020012: will-it-scale.per_thread_ops -12.2% regression

From: kernel test robot
Date: Thu Feb 21 2019 - 00:46:43 EST

On Thu, Feb 21, 2019 at 11:46:12AM +0800, Wei Yang wrote:
> On Thu, Feb 21, 2019 at 11:10:49AM +0800, kernel test robot wrote:
> >On Tue, Feb 19, 2019 at 01:19:04PM +0100, Greg Kroah-Hartman wrote:
> >> On Tue, Feb 19, 2019 at 08:59:45AM +0800, Wei Yang wrote:
> >> > On Mon, Feb 18, 2019 at 03:54:42PM +0800, kernel test robot wrote:
> >> > >Greeting,
> >> > >
> >> > >FYI, we noticed a -12.2% regression of will-it-scale.per_thread_ops due to commit:
> >> > >
> >> > >
> >> > >commit: 570d0200123fb4f809aa2f6226e93a458d664d70 ("driver core: move device->knode_class to device_private")
> >> > >https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> >> > >
> >> >
> >> > This is interesting.
> >> >
> >> > I didn't expect the move of this field will impact the performance.
> >> >
> >> > The reason is struct device is a hotter memory than device->device_private?
> >> >
> >> > >in testcase: will-it-scale
> >> > >on test machine: 288 threads Knights Mill with 80G memory
> >> > >with following parameters:
> >> > >
> >> > > nr_task: 100%
> >> > > mode: thread
> >> > > test: unlink2
> >> > > cpufreq_governor: performance
> >> > >
> >> > >test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
> >> > >test-url: https://github.com/antonblanchard/will-it-scale
> >> > >
> >> > >In addition to that, the commit also has significant impact on the following tests:
> >> > >
> >> > >+------------------+---------------------------------------------------------------+
> >> > >| testcase: change | will-it-scale: will-it-scale.per_thread_ops -29.9% regression |
> >> > >| test machine | 288 threads Knights Mill with 80G memory |
> >> > >| test parameters | cpufreq_governor=performance |
> >> > >| | mode=thread |
> >> > >| | nr_task=100% |
> >> > >| | test=signal1 |
> >>
> >> Ok, I'm going to blame your testing system, or something here, and not
> >> the above patch.
> >>
> >> All this test does is call raise(3). That does not touch the driver
> >> core at all.
> >>
> >> > >+------------------+---------------------------------------------------------------+
> >> > >| testcase: change | will-it-scale: will-it-scale.per_thread_ops -16.5% regression |
> >> > >| test machine | 288 threads Knights Mill with 80G memory |
> >> > >| test parameters | cpufreq_governor=performance |
> >> > >| | mode=thread |
> >> > >| | nr_task=100% |
> >> > >| | test=open1 |
> >> > >+------------------+---------------------------------------------------------------+
> >>
> >> Same here, open1 just calls open/close a lot. No driver core
> >> interaction at all there either.
> >>
> >> So are you _sure_ this is the offending patch?
> >
> >Hi Greg,
> >
> >We did an experiment, recovered the layout of struct device. and we
> >found the regression is gone. I guess the regession is not from the
> >patch but related to the struct layout.
> >
> >
> >tests: 1
> >testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-unlink2/lkp-knm01
> >
> >570d0200123fb4f8 a36dc70b810afe9183de2ea18f
> >---------------- --------------------------
> > %stddev change %stddev
> > \ | \
> > 237096 14% 270789 will-it-scale.workload
> > 823 14% 939 will-it-scale.per_thread_ops
> >
>
> Do you have the comparison between a36dc70b810afe9183de2ea18f and the one
> before 570d020012?

testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-unlink2/lkp-knm01

4bd4e92cfe6d2af7 a36dc70b810afe9183de2ea18f
---------------- --------------------------
%stddev %change %stddev
\ | \
937.00 +0.2% 939.33 will-it-scale.per_thread_ops
269989 +0.3% 270789 will-it-scale.workload

> >
> >tests: 1
> >testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-signal1/lkp-knm01
> >
> >570d0200123fb4f8 a36dc70b810afe9183de2ea18f
> >---------------- --------------------------
> > %stddev change %stddev
> > \ | \
> > 93.51 Â 3% 48% 138.53 Â 3% will-it-scale.time.user_time
> > 186 40% 261 will-it-scale.per_thread_ops
> > 53909 40% 75507 will-it-scale.workload
> >

testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-signal1/lkp-knm01

4bd4e92cfe6d2af7 a36dc70b810afe9183de2ea18f
---------------- --------------------------
%stddev %change %stddev
\ | \
266.00 Â 2% -1.6% 261.67 will-it-scale.per_thread_ops
76699 Â 2% -1.6% 75507 will-it-scale.workload

> >
> >tests: 1
> >testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-open1/lkp-knm01
> >
> >570d0200123fb4f8 a36dc70b810afe9183de2ea18f
> >---------------- --------------------------
> > %stddev change %stddev
> > \ | \
> > 447722 22% 546258 Â 10% will-it-scale.time.involuntary_context_switches
> > 226995 19% 269751 will-it-scale.workload
> > 787 19% 936 will-it-scale.per_thread_ops
> >
> >

testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-open1/lkp-knm01

4bd4e92cfe6d2af7 a36dc70b810afe9183de2ea18f
---------------- --------------------------
%stddev %change %stddev
\ | \
944.60 -0.9% 936.00 will-it-scale.per_thread_ops
272252 -0.9% 269751 will-it-scale.workload

Best Regards,
Rong Chen