linux-kernel - Re: [PATCH v4] sched: Fast idling of CPU when system is partially loaded

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <53A87E74.5090702@redhat.com>
Date:	Mon, 23 Jun 2014 15:22:28 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Davidlohr Bueso <davidlohr@...com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] sched: Fast idling of CPU when system is partially
 loaded

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 06/23/2014 03:16 PM, Tim Chen wrote:
> Thanks to the review from Jason, Andi and Peter. I've updated the
> code as Peter suggested with simplified logic.
> 
> When a system is lightly loaded (i.e. no more than 1 job per cpu), 
> attempt to pull job to a cpu before putting it to idle is
> unnecessary and can be skipped.  This patch adds an indicator so
> the scheduler can know when there's no more than 1 active job is on
> any CPU in the system to skip needless job pulls.
> 
> On a 4 socket machine with a request/response kind of workload
> from clients, we saw about 0.13 msec delay when we go through a
> full load balance to try pull job from all the other cpus.  While
> 0.1 msec was spent on processing the request and generating a
> response, the 0.13 msec load balance overhead was actually more
> than the actual work being done. This overhead can be skipped much
> of the time for lightly loaded systems.
> 
> With this patch, we tested with a netperf request/response workload
> that has the server busy with half the cpus in a 4 socket system.
> We found the patch eliminated 75% of the load balance attempts
> before idling a cpu.
> 
> The overhead of setting/clearing the indicator is low as we already
> gather the necessary info while we call add_nr_running and
> update_sd_lb_stats. We switch to full load balance load immediately
> if any cpu got more than one job on its run queue in
> add_nr_running.  We'll clear the indicator to avoid load balance
> when we detect no cpu's have more than one job when we scan the
> work queues in update_sg_lb_stats.  We are aggressive in turning on
> the load balance and opportunistic in skipping the load balance.
> 
> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com> Acked-by:
> Jason Low <jason.low2@...com>

Acked-by: Rik van Riel <riel@...hat.com>


- -- 
All rights reversed
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

iQEcBAEBAgAGBQJTqH50AAoJEM553pKExN6DYj4H/17YlyWg0QDoNrkNbhEi8SfD
I0BsklbbDIpcq9hKpwiJOCiQNeVLjMwhTniKOOXj1LgbtSsHYz7Scac/vt9sJRsy
PLJKoQt43lSv7Ff3mJFbUZG5u2RWoLs8TLuSFhPd39J8XupJX9jVe3GejBsp8lN4
Mpmo2DD6FvjvF2mpIP+CpEDFQZNeEZBb9UMvAJCjAU4JwdodwFkLRgxTWyOUSFpS
eOhDj99nRgyCz0LwLaVD2mfi29B/C5giIk70G+1II9BjTDGlFJC9X5FairZ3bM+K
6//BDq1baNnVu7pKKtQe8bLhNFQ1z1WNtgDr8L9c6dw9rLI+5AGjZb+KK5mMnG8=
=goKD
-----END PGP SIGNATURE-----
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/