Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932195Ab3CYOhd (ORCPT ); Mon, 25 Mar 2013 10:37:33 -0400 Received: from mail-la0-f51.google.com ([209.85.215.51]:58605 "EHLO mail-la0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932094Ab3CYOhc (ORCPT ); Mon, 25 Mar 2013 10:37:32 -0400 MIME-Version: 1.0 In-Reply-To: <0000013da1f6170e-7b247826-93a9-4c2d-a316-ba3b0597a805-000000@email.amazonses.com> References: <20130318222548.GG3656@linux.vnet.ibm.com> <1363822338.6345.33.camel@gandalf.local.home> <20130320235545.GL3637@linux.vnet.ibm.com> <0000013d8db514e4-bf492080-82c9-412a-90b8-54ddc1463e4b-000000@email.amazonses.com> <20130321171518.GW3637@linux.vnet.ibm.com> <0000013d8e3f58ce-0f6ea95f-780a-49c1-a633-5aa0cf3e5040-000000@email.amazonses.com> <20130321185821.GF3637@linux.vnet.ibm.com> <0000013d8e8d24fd-d2931c45-2722-46d1-8b47-2ef11e21096d-000000@email.amazonses.com> <20130321205054.GI3637@linux.vnet.ibm.com> <0000013d9289cebc-e6380265-3a74-4343-b851-765f785a3754-000000@email.amazonses.com> <20130322162820.GN3637@linux.vnet.ibm.com> <0000013da1f6170e-7b247826-93a9-4c2d-a316-ba3b0597a805-000000@email.amazonses.com> Date: Mon, 25 Mar 2013 15:37:30 +0100 Message-ID: Subject: Re: [PATCH] nohz1: Documentation From: Frederic Weisbecker To: Christoph Lameter Cc: "Paul E. McKenney" , Steven Rostedt , Rob Landley , linux-kernel@vger.kernel.org, josh@joshtriplett.org, zhong@linux.vnet.ibm.com, khilman@linaro.org, geoff@infradead.org, tglx@linutronix.de Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1315 Lines: 29 2013/3/25 Christoph Lameter : > On Fri, 22 Mar 2013, Paul E. McKenney wrote: > >> On Fri, Mar 22, 2013 at 02:38:58PM +0000, Christoph Lameter wrote: >> > On Thu, 21 Mar 2013, Paul E. McKenney wrote: >> > >> > > So, how long of busy periods are you contemplating for your SCHED_FIFO >> > > threads? Is it possible to tune/adjust the offending per-CPU ktheads >> > > to wake up less frequently than that time? >> > >> > Test programs right now run 10 seconds. 30 seconds would definitely be >> > enough for the worst case. >> >> OK, that might be doable for some workloads. What happens when you >> try tuning the 2-second wakeup interval to (say) 45 seconds? > > The vm kernel threads do no useful work if no system calls are being done. > If there is no kernel action then they can be deferred indefinitely. > We can certainly add some user deferrable timer_list. But that's going to be for extreme usecases (those who require pure isolation) because we'll need to settle that with a timer reprogramming into user/kernel boundaries. That won't be free. -- 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/