Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755887Ab3DOQSG (ORCPT ); Mon, 15 Apr 2013 12:18:06 -0400 Received: from a9-62.smtp-out.amazonses.com ([54.240.9.62]:46083 "EHLO a9-62.smtp-out.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755359Ab3DOQSE (ORCPT ); Mon, 15 Apr 2013 12:18:04 -0400 X-Greylist: delayed 379 seconds by postgrey-1.27 at vger.kernel.org; Mon, 15 Apr 2013 12:18:04 EDT Date: Mon, 15 Apr 2013 16:11:43 +0000 From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Ingo Molnar cc: Frederic Weisbecker , "Paul E. McKenney" , LKML , Andrew Morton , Chris Metcalf , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Kevin Hilman , Li Zhong , Namhyung Kim , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner Subject: Re: [PATCH 4/4] nohz: New option to force all CPUs in full dynticks range In-Reply-To: <20130415102750.GE18024@gmail.com> Message-ID: <0000013e0e7759a3-5b08a307-9a47-49de-b1cf-d00306df0f6d-000000@email.amazonses.com> References: <20130328074507.GC24433@gmail.com> <20130330091037.GA31743@gmail.com> <0000013dea26b171-8095c339-dc81-4459-a3ad-a8d69c803448-000000@email.amazonses.com> <20130411151956.GF15699@somewhere> <20130411153721.GA3742@linux.vnet.ibm.com> <20130411155349.GA16797@somewhere.redhat.com> <0000013df9f8d526-2783fba3-4dc9-44c6-8b02-2c321eb5b37b-000000@email.amazonses.com> <20130411170420.GA17129@somewhere.redhat.com> <0000013dfef98b2d-ed5980b1-86ff-47de-8aa1-fd7fdd02f034-000000@email.amazonses.com> <20130415102750.GE18024@gmail.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-SES-Outgoing: 2013.04.15-54.240.9.62 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1343 Lines: 32 On Mon, 15 Apr 2013, Ingo Molnar wrote: > > Ok. But all these complicated things would go away if we had an option > > CONFIG_LOWLATENCY and then everything would just follow the best setup > > possible given the hardware. Would remove a lot of guesswork and a lot of > > knobs. > > In that sense CONFIG_NO_HZ_FULL is such a flag as well, which, like > CONFIG_PREEMPT_RT, tries to preconfigure the kernel correctly. It is too specific. Switching off HZ is one in a set of measures that one woiuld take. F.e. the page allocator will want to do reclaim on the sacrificial processor, the vmstatistics would run their monitoring thread there etc etc. > But we have to be careful not to use a too highlevel flag for that. If the user > meant 'low latency' to mean 'low latency IRQ execution' - then enabling > CONFIG_NO_HZ_FULL might achieve the opposite, it adds overhead to the IRQ paths. Hmm.... Looks too specific for my taste. What the user wants is less OS noise (or maybe some other terms that describes that the user wants minimal disturbances for his code). CONFIG_OS_NOISE_REDUCTION ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/