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Date: Thu, 21 Feb 2019 12:46:18 +0800
From: "Huang\, Ying" <ying.huang@...el.com>
To: Wei Yang <richardw.yang@...ux.intel.com>
Cc: kernel test robot <rong.a.chen@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Stephen Rothwell <sfr@...b.auug.org.au>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, <lkp@...org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LKP] [driver core] 570d020012: will-it-scale.per_thread_ops -12.2% regression
Wei Yang <richardw.yang@...ux.intel.com> writes:
> 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?
>
>>
>>tests: 1
>>testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-signal1/lkp-knm01
>>
>>570d0200123fb4f8 a36dc70b810afe9183de2ea18f
>>---------------- --------------------------
>> %stddev change %stddev
>> \ | \
>> 93.51 3% 48% 138.53 3% will-it-scale.time.user_time
>> 186 40% 261 will-it-scale.per_thread_ops
>> 53909 40% 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 10% will-it-scale.time.involuntary_context_switches
>> 226995 19% 269751 will-it-scale.workload
>> 787 19% 936 will-it-scale.per_thread_ops
>>
>>
>>
>>commit a36dc70b810afe9183de2ea18faa4c0939c139ac
>>Author: 0day robot <lkp@...el.com>
>>Date: Wed Feb 20 14:21:19 2019 +0800
>>
>> backfile klist_node in struct device for debugging
>>
>> Signed-off-by: 0day robot <lkp@...el.com>
>>
>>diff --git a/include/linux/device.h b/include/linux/device.h
>>index d0e452fd0bff2..31666cb72b3ba 100644
>>--- a/include/linux/device.h
>>+++ b/include/linux/device.h
>>@@ -1035,6 +1035,7 @@ struct device {
>> spinlock_t devres_lock;
>> struct list_head devres_head;
>>
>>+ struct klist_node knode_class_test_by_rongc;
>> struct class *class;
>> const struct attribute_group **groups; /* optional groups */
>
> Hmm... because this is not properly aligned?
>
> struct klist_node {
> void *n_klist; /* never access directly */
> struct list_head n_node;
> struct kref n_ref;
> };
>
> Except struct kref has one "int" type, others are pointers.
>
> But... I am still confused.
I guess because the size of struct device is changed, it influences some
alignment changes in the system. Thus influence the benchmark score.
Best Regards,
Huang, Ying
>>
>>Best Regards,
>>Rong Chen
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