linux-kernel - Re: [RFC][PATCH 00/26] sched/numa

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: <4F67546A.9060803@redhat.com>
Date:	Mon, 19 Mar 2012 17:44:42 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dan Smith <danms@...ibm.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 00/26] sched/numa

On 03/19/2012 02:24 PM, Avi Kivity wrote:
> On 03/19/2012 02:20 PM, Peter Zijlstra wrote:
> > On Mon, 2012-03-19 at 13:42 +0200, Avi Kivity wrote:
> > > It's the standard space/time tradeoff.  Once solution wants more
> > > storage, the other wants more faults.
> > > 
> > > Note scanners can use A/D bits which are cheaper than faults.
> >
> > I'm not convinced.. the scanner will still consume time even if the
> > system is perfectly balanced -- it has to in order to determine this.
> >
> > So sure, A/D/other page table magic can make scanners faster than faults
> > however you only need faults when you're actually going to migrate a
> > task. Whereas you always need to scan, even in the stable state.
> >
> > So while the per-instance times might be in favour of scanning, I'm
> > thinking the accumulated time is in favour of faults.
>
> When you migrate a vnode, you don't need the faults at all.  You know
> exactly which pages need to be migrated, you can just queue them
> immediately when you make that decision.
>
> The scanning therefore only needs to pick up the stragglers and can be
> set to a very low frequency.

Running the numbers, 4GB = 1Mpages, at 2us per page migration that's 2
seconds to migrate an entire process, perhaps 2x-3x that for kvm.  So as
long numa balancing happens at a lower frequency than once every few
minutes, the gains should be higher than the loss.  If those numbers are
not too wrong then migrate on fault should be a win.

-- 
error compiling committee.c: too many arguments to function

--
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/