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Message-ID: <20160620000606.GB3194@blaptop>
Date: Mon, 20 Jun 2016 09:06:06 +0900
From: Minchan Kim <minchan@...nel.org>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Minchan Kim <minchan@...nel.org>,
"Kirill A. Shutemov" <kirill@...temov.name>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Rik van Riel <riel@...hat.com>,
Michal Hocko <mhocko@...e.com>,
LKML <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Michal Hocko <mhocko@...nel.org>,
Vinayak Menon <vinmenon@...eaurora.org>,
Mel Gorman <mgorman@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>, lkp@...org,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [LKP] [lkp] [mm] 5c0a85fad9: unixbench.score -6.3% regression
On Fri, Jun 17, 2016 at 12:26:51PM -0700, Huang, Ying wrote:
> Minchan Kim <minchan@...nel.org> writes:
>
> > On Thu, Jun 16, 2016 at 03:27:44PM -0700, Huang, Ying wrote:
> >> Minchan Kim <minchan@...nel.org> writes:
> >>
> >> > On Thu, Jun 16, 2016 at 07:52:26AM +0800, Huang, Ying wrote:
> >> >> "Kirill A. Shutemov" <kirill@...temov.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@...el.com> writes:
> >> >> >> > >
> >> >> >> > > > "Kirill A. Shutemov" <kirill.shutemov@...ux.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.
> >>
> >
> > Thanks for the testing!
> >
> > nr_active_file was shrunk 48% but the vaule itself is not huge so
> > I don't think it affects performance a lot.
> >
> > There was no reclaim activity for testing. :(
> >
> > pgfault, 6% reduced. Given that, pgalloc/free reduced 6%, too
> > because unixbench was time fixed mode and 6% regressed so no
> > doubt.
> >
> > No interesting data.
> >
> > It seems you tested it with THP, maybe always mode?
>
> Yes. With following in kconfig.
>
> CONFIG_TRANSPARENT_HUGEPAGE=y
> CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
>
> > I'm so sorry but could you test it with disabling CONFIG_TRANSPARENT_HUGEPAGE=n
> > again? it might you already did.
> > Is it still 6% regressed with disabling THP?
>
> Yes. I disabled THP via
>
> echo never > /sys/kernel/mm/transparent_hugepage/enabled
> echo never > /sys/kernel/mm/transparent_hugepage/defrag
>
> The regression is the same as before.
Still, 6% user_time regression and there is no difference with previous
experiment which enabled THP so I agree the regression is caused by just
access bit setting from CPU side, which is rather surprising to me.
I don't know how unixbench shell scripts testing touch the memory
but it should be per-page overhead and 6% regression for that is too heavy.
Anyway, at least, it would be better to notice it to x86 maintainer.
Thanks for the test!
>
> =========================================================================================
> compiler/cpufreq_governor/kconfig/nr_task/rootfs/tbox_group/test/testcase/thp_defrag/thp_enabled:
> gcc-4.9/performance/x86_64-rhel/1/debian-x86_64-2015-02-07.cgz/lituya/shell8/unixbench/never/never
>
> commit:
> 4b50bcc7eda4d3cc9e3f2a0aa60e590fedf728c5
> 5c0a85fad949212b3e059692deecdeed74ae7ec7
>
> 4b50bcc7eda4d3cc 5c0a85fad949212b3e059692de
> ---------------- --------------------------
> %stddev %change %stddev
> \ | \
> 14332 ± 0% -6.2% 13438 ± 0% unixbench.score
> 6662206 ± 0% -6.2% 6252260 ± 0% unixbench.time.involuntary_context_switches
> 5.734e+08 ± 0% -6.2% 5.376e+08 ± 0% unixbench.time.minor_page_faults
> 2527 ± 0% -3.2% 2446 ± 0% unixbench.time.system_time
> 1291 ± 0% +5.4% 1361 ± 0% unixbench.time.user_time
> 19875455 ± 0% -6.3% 18622488 ± 0% unixbench.time.voluntary_context_switches
> 6570355 ± 0% -11.9% 5787517 ± 0% cpuidle.C1-HSW.usage
> 17257 ± 34% -59.1% 7055 ± 7% latency_stats.sum.ep_poll.SyS_epoll_wait.entry_SYSCALL_64_fastpath
> 5976 ± 0% -43.0% 3404 ± 0% proc-vmstat.nr_active_file
> 45729 ± 1% -22.5% 35439 ± 1% meminfo.Active
> 23905 ± 0% -43.0% 13619 ± 0% meminfo.Active(file)
> 8465 ± 3% -29.8% 5940 ± 3% slabinfo.pid.active_objs
> 8476 ± 3% -29.9% 5940 ± 3% slabinfo.pid.num_objs
> 3.46 ± 0% +12.5% 3.89 ± 0% turbostat.CPU%c3
> 67.09 ± 0% -2.1% 65.65 ± 0% turbostat.PkgWatt
> 96090 ± 0% -5.8% 90479 ± 0% vmstat.system.cs
> 9083 ± 0% -2.7% 8833 ± 0% vmstat.system.in
> 467.35 ± 78% +416.7% 2414 ± 45% sched_debug.cfs_rq:/.MIN_vruntime.avg
> 7477 ± 78% +327.7% 31981 ± 39% sched_debug.cfs_rq:/.MIN_vruntime.max
> 1810 ± 78% +360.1% 8327 ± 40% sched_debug.cfs_rq:/.MIN_vruntime.stddev
> 467.35 ± 78% +416.7% 2414 ± 45% sched_debug.cfs_rq:/.max_vruntime.avg
> 7477 ± 78% +327.7% 31981 ± 39% sched_debug.cfs_rq:/.max_vruntime.max
> 1810 ± 78% +360.1% 8327 ± 40% sched_debug.cfs_rq:/.max_vruntime.stddev
> -10724 ± -7% -12.0% -9433 ± -3% sched_debug.cfs_rq:/.spread0.avg
> -17721 ± -4% -9.8% -15978 ± -2% sched_debug.cfs_rq:/.spread0.min
> 90355 ± 9% +14.1% 103099 ± 5% sched_debug.cpu.avg_idle.min
> 0.12 ± 35% +325.0% 0.52 ± 46% sched_debug.cpu.cpu_load[0].min
> 21913 ± 2% +29.1% 28288 ± 14% sched_debug.cpu.curr->pid.avg
> 49953 ± 3% +30.2% 65038 ± 0% sched_debug.cpu.curr->pid.max
> 23062 ± 2% +30.1% 29996 ± 4% sched_debug.cpu.curr->pid.stddev
> 274.39 ± 5% -10.2% 246.27 ± 3% sched_debug.cpu.nr_uninterruptible.max
> 242.73 ± 4% -13.5% 209.90 ± 2% sched_debug.cpu.nr_uninterruptible.stddev
>
> Best Regards,
> Huang, Ying
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