linux-kernel - Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq

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: <20130222121123.GA6473@gmail.com>
Date:	Fri, 22 Feb 2013 13:11:23 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Galbraith <efault@....de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, alex.shi@...el.com,
	Ram Pai <linuxram@...ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()


* Mike Galbraith <efault@....de> wrote:

> On Fri, 2013-02-22 at 10:54 +0100, Ingo Molnar wrote: 
> > * Mike Galbraith <efault@....de> wrote:
> > 
> > > On Fri, 2013-02-22 at 09:36 +0100, Peter Zijlstra wrote: 
> > > > On Fri, 2013-02-22 at 10:37 +0800, Michael Wang wrote:
> > > > > But that's really some benefit hardly to be estimate, especially when
> > > > > the workload is heavy, the cost of wake_affine() is very high to
> > > > > calculated se one by one, is that worth for some benefit we could not
> > > > > promise?
> > > > 
> > > > Look at something like pipe-test.. wake_affine() used to 
> > > > ensure both client/server ran on the same cpu, but then I 
> > > > think we added select_idle_sibling() and wrecked it again :/
> > > 
> > > Yeah, that's the absolute worst case for 
> > > select_idle_sibling(), 100% synchronous, absolutely nothing to 
> > > be gained by cross cpu scheduling. Fortunately, most tasks do 
> > > more than that, but nonetheless, select_idle_sibling() 
> > > definitely is a two faced little b*tch.  I'd like to see the 
> > > evil b*tch die, but something needs to replace it's pretty 
> > > face.  One thing that you can do is simply don't call it when 
> > > the context switch rate is incredible.. its job is to recover 
> > > overlap, if you're scheduling near your max, there's no win 
> > > worth the cost.
> > 
> > Couldn't we make the cutoff dependent on sched_migration_cost? 
> > If the wakeup comes in faster than that then don't spread.
> 
> No, that's too high, you loose too much of the pretty face. 
> [...]

Then a logical proportion of it - such as half of it?

Thanks,

	Ingo
--
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/