linux-kernel - Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry

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Date:	Sun, 03 May 2015 15:23:52 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, williams@...hat.com, luto@...nel.org,
	fweisbec@...hat.com, peterz@...radead.org,
	heiko.carstens@...ibm.com, tglx@...utronix.de,
	Ingo Molnar <mingo@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable
 & enable from context tracking on syscall entry

On Fri, 2015-05-01 at 11:20 -0400, Rik van Riel wrote:
> On 05/01/2015 02:40 AM, Ingo Molnar wrote:
> 
> >> This patch builds on top of these patches by Paolo:
> >> https://lkml.org/lkml/2015/4/28/188
> >> https://lkml.org/lkml/2015/4/29/139
> >>
> >> Together with this patch I posted earlier this week, the syscall path
> >> on a nohz_full cpu seems to be about 10% faster.
> >> https://lkml.org/lkml/2015/4/24/394
> >>
> >> My test is a simple microbenchmark that calls getpriority() in a loop
> >> 10 million times:
> >>
> >> 		run time	system time
> >> vanilla		5.49s		2.08s
> >> __acct patch	5.21s		1.92s
> >> both patches	4.88s		1.71s
> >
> > Just curious, what are the numbers if you don't have context tracking 
> > enabled, i.e. without nohz_full?
> > 
> > I.e. what's the baseline we are talking about?
> 
> It's an astounding difference. This is not a kernel without nohz_full,
> just a CPU without nohz_full running the same kernel I tested with
> yesterday:
> 
>  		run time	system time
> vanilla		5.49s		2.08s
> __acct patch	5.21s		1.92s
> both patches	4.88s		1.71s
> CPU w/o nohz	3.12s		1.63s    <-- your numbers, mostly

Below are v4.1-rc1-172-g6c3c1eb3c35e + patches measurements.

100M * stat() on isolated cpu

NO_HZ_FULL off        inactive     housekeeper    nohz_full
real    0m14.266s     0m14.367s    0m20.427s      0m27.921s
user    0m1.756s      0m1.553s     0m1.976s       0m10.447s
sys     0m12.508s     0m12.769s    0m18.400s      0m17.464s
(real)  1.000         1.007        1.431          1.957
                                   1.000          1.000

                         real      0m20.423s      0m27.930s  +rik 1,2
                         user      0m2.072s       0m10.450s
                         sys       0m18.304s      0m17.471s
                         vs off    1.431          1.957
                         vs prev   1.000          1.000

                         real      0m20.256s      0m27.803s  +paolo 1,2 (2 missing prototypes)
                         user      0m1.884s       0m10.551s
                         sys       0m18.353s      0m17.242s
                         vs off    1.419          1.948
                         vs prev    .991           .995

                         real      0m19.122s      0m26.946s  +rik 3
                         user      0m1.896s       0m10.292s
                         sys       0m17.198s      0m16.644s
                         vs off    1.340          1.888
                         vs prev   .944            .969



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