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

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

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