linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Huang\, Ying" <ying.huang@intel.com>
To: Minchan Kim <minchan@kernel.org>
Cc: "Huang\, Ying" <ying.huang@intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Rik van Riel <riel@redhat.com>, "Michal Hocko" <mhocko@suse.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@kernel.org>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Mel Gorman <mgorman@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>, LKP <lkp@01.org>
Subject: Re: [LKP] [lkp] [mm] 5c0a85fad9: unixbench.score -6.3% regression
Date: Thu, 16 Jun 2016 07:42:07 +0800	[thread overview]
Message-ID: <87bn32xbn4.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20160614133807.GA16342@bbox> (Minchan Kim's message of "Tue, 14 Jun 2016 22:38:07 +0900")

Minchan Kim <minchan@kernel.org> writes:

> On Mon, Jun 13, 2016 at 05:02:15PM +0800, Huang, Ying wrote:
>> Linus Torvalds <torvalds@linux-foundation.org> writes:
>> 
>> > On Sat, Jun 11, 2016 at 5:49 PM, Huang, Ying <ying.huang@intel.com> wrote:
>> >>
>> >> From perf profile, the time spent in page_fault and its children
>> >> functions are almost same (7.85% vs 7.81%).  So the time spent in page
>> >> fault and page table operation itself doesn't changed much.  So, you
>> >> mean CPU may be slower to load the page table entry to TLB if accessed
>> >> bit is not set?
>> >
>> > So the CPU does take a microfault internally when it needs to set the
>> > accessed/dirty bit. It's not architecturally visible, but you can see
>> > it when you do timing loops.
>> >
>> > I've timed it at over a thousand cycles on at least some CPU's, but
>> > that's still peanuts compared to a real page fault. It shouldn't be
>> > *that* noticeable, ie no way it's a 6% regression on its own.
>> 
>> I done some simple counting, and found that about 3.15e9 PTE are set to
>> old during the test after the commit.  This may interpret the user_time
>> increase as below, because these accessed bit microfault is accounted as
>> user time.
>> 
>>     387.66 .  0%      +5.4%     408.49 .  0%  unixbench.time.user_time
>> 
>> I also make a one line debug patch as below on top of the commit to set
>> the PTE to young unconditionally, which recover the regression.
>
> With this patch, meminfo.Active(file) is almost same unlike previous
> experiment?

Yes.  meminfo.Active(file) is almost same of that of the parent commit of
the first bad commit.

Best Regards,
Huang, Ying

>> 
>> modified   mm/filemap.c
>> @@ -2193,7 +2193,7 @@ repeat:
>>  		if (file->f_ra.mmap_miss > 0)
>>  			file->f_ra.mmap_miss--;
>>  		addr = address + (page->index - vmf->pgoff) * PAGE_SIZE;
>> -		do_set_pte(vma, addr, page, pte, false, false, true);
>> +		do_set_pte(vma, addr, page, pte, false, false, false);
>>  		unlock_page(page);
>>  		atomic64_inc(&old_pte_count);
>>  		goto next;
>> 
>> Best Regards,
>> Huang, Ying

  reply	other threads:[~2016-06-15 23:42 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-06  2:27 kernel test robot
2016-06-06  9:51 ` Kirill A. Shutemov
2016-06-08  7:21   ` [LKP] " Huang, Ying
2016-06-08  8:41     ` Huang, Ying
2016-06-08  8:58       ` Kirill A. Shutemov
2016-06-12  0:49         ` Huang, Ying
2016-06-12  1:02           ` Linus Torvalds
2016-06-13  9:02             ` Huang, Ying
2016-06-14 13:38               ` Minchan Kim
2016-06-15 23:42                 ` Huang, Ying [this message]
2016-06-13 12:52             ` Kirill A. Shutemov
2016-06-14  6:11               ` Linus Torvalds
2016-06-14  8:26                 ` Kirill A. Shutemov
2016-06-14 16:07                   ` Rik van Riel
2016-06-14 14:03                 ` Christian Borntraeger
2016-06-14  8:57         ` Minchan Kim
2016-06-14 14:34           ` Kirill A. Shutemov
2016-06-15 23:52             ` Huang, Ying
2016-06-16  0:13               ` Minchan Kim
2016-06-16 22:27                 ` Huang, Ying
2016-06-17  5:41                   ` Minchan Kim
2016-06-17 19:26                     ` Huang, Ying
2016-06-20  0:06                       ` Minchan Kim

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87bn32xbn4.fsf@yhuang-dev.intel.com \
    --to=ying.huang@intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=kirill.shutemov@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lkp@01.org \
    --cc=mgorman@suse.de \
    --cc=mhocko@kernel.org \
    --cc=mhocko@suse.com \
    --cc=minchan@kernel.org \
    --cc=riel@redhat.com \
    --cc=torvalds@linux-foundation.org \
    --cc=vinmenon@codeaurora.org \
    --subject='Re: [LKP] [lkp] [mm] 5c0a85fad9: unixbench.score -6.3% regression' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).