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From: Minchan Kim <minchan@kernel.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: 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: Tue, 14 Jun 2016 22:38:07 +0900	[thread overview]
Message-ID: <20160614133807.GA16342@bbox> (raw)
In-Reply-To: <87bn35zcko.fsf@yhuang-dev.intel.com>

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?

> 
> 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:[~2016-06-14 13:38 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 [this message]
2016-06-15 23:42                 ` Huang, Ying
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

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