linux-kernel - Re: [RFC PATCH] sched: Reduce overestimating avg

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] [day] [month] [year] [list]

Message-ID: <1375431605.8749.34.camel@j-VirtualBox>
Date:	Fri, 02 Aug 2013 01:20:05 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, KML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	aswin@...com, scott.norton@...com, chegu_vinod@...com,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH] sched: Reduce overestimating avg_idle

On Wed, 2013-07-31 at 11:53 +0200, Peter Zijlstra wrote:

> No they're quite unrelated. I think you can measure the max time we've
> ever spend in newidle balance and use that to clip the values.

So I tried using the rq's max newidle balance cost to compare with the
average and used sysctl_migration_cost as the initial/default max. One
thing I noticed when running this on 8 socket machine was that the max
idle balance cost was a lot higher during around boot time compared to
after boot time. Not sure if IRQ/NMI/SMI was the cause of this. A
temporary "fix" I made was to reset the max idle balance costs every 2
minutes.

> Similarly, I've thought about how we updated the sd->avg_cost in the
> previous patches and wondered if we should not track max_cost.
> 
> The 'only' down-side I could come up with is that its all ran from
> SoftIRQ context which means IRQ/NMI/SMI can all stretch/warp the time it
> takes to actually do the idle balance.

Another thing that I thought of was that max idle balance cost may also
vary based on the workload that is running. So running a workload in
which there are shorter idle balances after running a workload that has
longer idle balances may sometimes cause it to make use of a higher idle
balance cost. But I guess it is okay if we're trying to reduce
overrunning the average.

Jason

--
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/