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Message-ID: <20190221075313.GA4113@richard>
Date: Thu, 21 Feb 2019 15:53:13 +0800
From: Wei Yang <richardw.yang@...ux.intel.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
kernel test robot <rong.a.chen@...el.com>,
Wei Yang <richardw.yang@...ux.intel.com>,
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
On Thu, Feb 21, 2019 at 03:18:22PM +0800, Huang, Ying wrote:
>Greg Kroah-Hartman <gregkh@...uxfoundation.org> 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
>>>
>>>
>>> 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 */
>>
>> While this is fun to worry about alignment and structure size of 'struct
>> device' I find it odd given that the syscalls and userspace load of
>> those test programs have nothing to do with 'struct device' at all.
>>
>> So I can work on fixing up the alignment of struct device, as that's a
>> nice thing to do for systems with 30k of these in memory, but that
>> shouldn't affect a workload of a constant string of signal calls.
>
>Hi, Greg,
>
>I don't think this is an issues of struct device. As you said, struct
>device isn't access much during test. Struct device may share slab page
>with some other data structures (signal related, or fd related (as in
>some other test cases)), so that the alignment of these data structures
>are affected, so caused the performance regression.
>
I didn't get the point here neither.
slab allocator ask memory from page allocator Page by Page and split the page
into pre-defined size. For example, 128B, 512B... Just as shown in
/proc/slabinfo.
Per my understanding, each struct device / device_private will sits in its own
aligned space. struct device would sits in 1K slab and struct device_private
would sits in 256B slab, both before and after this patch if I am correct.
Hmm... I am just curious about how this alignment is affected. Maybe I lost
some point?
>Best Regards,
>Huang, Ying
>
>> thanks,
>>
>> greg k-h
--
Wei Yang
Help you, Help me
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