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

[Minchan Kim]

On Thu, Jun 16, 2016 at 07:52:26AM +0800, Huang, Ying wrote:
> "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> 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@xxxxxxxxx> writes:
> >> > > 
> >> > > > "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> 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.

Thanks.