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

thanks,

greg k-h

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