Re: [LKP] [lkp] [mm] 5c0a85fad9: unixbench.score -6.3% regression

["Huang\, Ying" <ying.huang@intel.com>]

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Minchan Kim <minchan@kernel.org> writes:

> On Thu, Jun 16, 2016 at 07:52:26AM +0800, Huang, Ying wrote:
>> "Kirill A. Shutemov" <kirill@shutemov.name> writes:
>> 
>> > On Tue, Jun 14, 2016 at 05:57:28PM +0900, Minchan Kim wrote:
>> >> On Wed, Jun 08, 2016 at 11:58:11AM +0300, Kirill A. Shutemov wrote:
>> >> > On Wed, Jun 08, 2016 at 04:41:37PM +0800, Huang, Ying wrote:
>> >> > > "Huang, Ying" <ying.huang@intel.com> writes:
>> >> > > 
>> >> > > > "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> writes:
>> >> > > >
>> >> > > >> On Mon, Jun 06, 2016 at 10:27:24AM +0800, kernel test robot wrote:
>> >> > > >>> 
>> >> > > >>> FYI, we noticed a -6.3% regression of unixbench.score due to commit:
>> >> > > >>> 
>> >> > > >>> commit 5c0a85fad949212b3e059692deecdeed74ae7ec7 ("mm: make faultaround produce old ptes")
>> >> > > >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> >> > > >>> 
>> >> > > >>> in testcase: unixbench
>> >> > > >>> on test machine: lituya: 16 threads Haswell High-end Desktop (i7-5960X 3.0G) with 16G memory
>> >> > > >>> with following parameters: cpufreq_governor=performance/nr_task=1/test=shell8
>> >> > > >>> 
>> >> > > >>> 
>> >> > > >>> Details are as below:
>> >> > > >>> -------------------------------------------------------------------------------------------------->
>> >> > > >>> 
>> >> > > >>> 
>> >> > > >>> =========================================================================================
>> >> > > >>> compiler/cpufreq_governor/kconfig/nr_task/rootfs/tbox_group/test/testcase:
>> >> > > >>>   gcc-4.9/performance/x86_64-rhel/1/debian-x86_64-2015-02-07.cgz/lituya/shell8/unixbench
>> >> > > >>> 
>> >> > > >>> commit: 
>> >> > > >>>   4b50bcc7eda4d3cc9e3f2a0aa60e590fedf728c5
>> >> > > >>>   5c0a85fad949212b3e059692deecdeed74ae7ec7
>> >> > > >>> 
>> >> > > >>> 4b50bcc7eda4d3cc 5c0a85fad949212b3e059692de 
>> >> > > >>> ---------------- -------------------------- 
>> >> > > >>>        fail:runs  %reproduction    fail:runs
>> >> > > >>>            |             |             |    
>> >> > > >>>           3:4          -75%            :4     kmsg.DHCP/BOOTP:Reply_not_for_us,op[#]xid[#]
>> >> > > >>>          %stddev     %change         %stddev
>> >> > > >>>              \          |                \  
>> >> > > >>>      14321 .  0%      -6.3%      13425 .  0%  unixbench.score
>> >> > > >>>    1996897 .  0%      -6.1%    1874635 .  0%  unixbench.time.involuntary_context_switches
>> >> > > >>>  1.721e+08 .  0%      -6.2%  1.613e+08 .  0%  unixbench.time.minor_page_faults
>> >> > > >>>     758.65 .  0%      -3.0%     735.86 .  0%  unixbench.time.system_time
>> >> > > >>>     387.66 .  0%      +5.4%     408.49 .  0%  unixbench.time.user_time
>> >> > > >>>    5950278 .  0%      -6.2%    5583456 .  0%  unixbench.time.voluntary_context_switches
>> >> > > >>
>> >> > > >> That's weird.
>> >> > > >>
>> >> > > >> I don't understand why the change would reduce number or minor faults.
>> >> > > >> It should stay the same on x86-64. Rise of user_time is puzzling too.
>> >> > > >
>> >> > > > unixbench runs in fixed time mode.  That is, the total time to run
>> >> > > > unixbench is fixed, but the work done varies.  So the minor_page_faults
>> >> > > > change may reflect only the work done.
>> >> > > >
>> >> > > >> Hm. Is reproducible? Across reboot?
>> >> > > >
>> >> > > 
>> >> > > And FYI, there is no swap setup for test, all root file system including
>> >> > > benchmark files are in tmpfs, so no real page reclaim will be
>> >> > > triggered.  But it appears that active file cache reduced after the
>> >> > > commit.
>> >> > > 
>> >> > >     111331 .  1%     -13.3%      96503 .  0%  meminfo.Active
>> >> > >      27603 .  1%     -43.9%      15486 .  0%  meminfo.Active(file)
>> >> > > 
>> >> > > I think this is the expected behavior of the commit?
>> >> > 
>> >> > Yes, it's expected.
>> >> > 
>> >> > After the change faularound would produce old pte. It means there's more
>> >> > chance for these pages to be on inactive lru, unless somebody actually
>> >> > touch them and flip accessed bit.
>> >> 
>> >> Hmm, tmpfs pages should be in anonymous LRU list and VM shouldn't scan
>> >> anonymous LRU list on swapless system so I really wonder why active file
>> >> LRU is shrunk.
>> >
>> > Hm. Good point. I don't why we have anything on file lru if there's no
>> > filesystems except tmpfs.
>> >
>> > Ying, how do you get stuff to the tmpfs?
>> 
>> We put root file system and benchmark into a set of compressed cpio
>> archive, then concatenate them into one initrd, and finally kernel use
>> that initrd as initramfs.
>
> I see.
>
> Could you share your 4 full vmstat(/proc/vmstat) files?
>
> old:
>
> cat /proc/vmstat > before.old.vmstat
> do benchmark
> cat /proc/vmstat > after.old.vmstat
>
> new:
>
> cat /proc/vmstat > before.new.vmstat
> do benchmark
> cat /proc/vmstat > after.new.vmstat
>
> IOW, I want to see stats related to reclaim.

Hi,

The /proc/vmstat for the parent commit (parent-proc-vmstat.gz) and first
bad commit (fbc-proc-vmstat.gz) are attached with the email.

The contents of the file is more than the vmstat before and after
benchmark running, but are sampled every 1 seconds.  Every sample begin
with "time: <time>".  You can check the first and last samples.  The
first /proc/vmstat capturing is started at the same time of the
benchmark, so it is not exactly the vmstat before the benchmark running.


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Best Regards,
Huang, Ying