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 13:30:21 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mike Galbraith <umgwanakikbuti@...il.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 05/03/2015 09:23 AM, Mike Galbraith wrote:

> 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

I'm convinced.

Time to try the remote sampling of CPU use statistics, and
lighten up the RCU overhead of context tracking.

I should be able to start on the remote sampling of CPU use
statistics this week.

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