Re: [lkp-robot] [mm] 7674270022: will-it-scale.per_process_ops -19.3% regression

From: Minchan Kim <minchan@kernel.org>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Ye Xiaolong <xiaolong.ye@intel.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>,
	Russell King <linux@armlinux.org.uk>,
	Tony Luck <tony.luck@intel.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	"David S. Miller" <davem@davemloft.net>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Jeff Dike <jdike@addtoit.com>,
	linux-arch@vger.kernel.org, lkp@01.org
Subject: Re: [lkp-robot] [mm]  7674270022:  will-it-scale.per_process_ops -19.3% regression
Date: Thu, 10 Aug 2017 13:20:40 +0900	[thread overview]
Message-ID: <20170810042040.GA2249@bbox> (raw)
In-Reply-To: <80589593-6F0E-4421-9279-681D5B388100@gmail.com>

On Wed, Aug 09, 2017 at 09:14:50PM -0700, Nadav Amit wrote:

Hi Nadav,

< snip >

> >>>>> According to the description it is "testcase:brk increase/decrease of one
> >>>>> pagea??. According to the mode it spawns multiple processes, not threads.
> >>>>> 
> >>>>> Since a single page is unmapped each time, and the iTLB-loads increase
> >>>>> dramatically, I would suspect that for some reason a full TLB flush is
> >>>>> caused during do_munmap().
> >>>>> 
> >>>>> If I find some free time, Ia??ll try to profile the workload - but feel free
> >>>>> to beat me to it.
> >>>> 
> >>>> The root-cause appears to be that tlb_finish_mmu() does not call
> >>>> dec_tlb_flush_pending() - as it should. Any chance you can take care of it?
> >>> 
> >>> Oops, but with second looking, it seems it's not my fault. ;-)
> >>> https://marc.info/?l=linux-mm&m=150156699114088&w=2
> >>> 
> >>> Anyway, thanks for the pointing out.
> >>> xiaolong.ye, could you retest with this fix?
> >> 
> >> I've queued tests for 5 times and results show this patch (e8f682574e4 "mm:
> >> decrease tlb flush pending count in tlb_finish_mmu") does help recover the
> >> performance back.
> >> 
> >> 378005bdbac0a2ec  76742700225cad9df49f053993  e8f682574e45b6406dadfffeb4  
> >> ----------------  --------------------------  --------------------------  
> >>         %stddev      change         %stddev      change         %stddev
> >>             \          |                \          |                \  
> >>   3405093             -19%    2747088              -2%    3348752        will-it-scale.per_process_ops
> >>      1280 A+-  3%        -2%       1257 A+-  3%        -6%       1207        vmstat.system.cs
> >>      2702 A+- 18%        11%       3002 A+- 19%        17%       3156 A+- 18%  numa-vmstat.node0.nr_mapped
> >>     10765 A+- 18%        11%      11964 A+- 19%        17%      12588 A+- 18%  numa-meminfo.node0.Mapped
> >>      0.00 A+- 47%       -40%       0.00 A+- 45%       -84%       0.00 A+- 42%  mpstat.cpu.soft%
> >> 
> >> Thanks,
> >> Xiaolong
> > 
> > Thanks for the testing!
> 
> Sorry again for screwing your patch, Minchan.

Never mind! It always happens. :)
In this chance, I really appreciates your insight/testing/cooperation!

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