From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932320AbbELJuj (ORCPT ); Tue, 12 May 2015 05:50:39 -0400 Received: from mail-wg0-f54.google.com ([74.125.82.54]:33804 "EHLO mail-wg0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752871AbbELJug (ORCPT ); Tue, 12 May 2015 05:50:36 -0400 Date: Tue, 12 May 2015 11:50:30 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: Chris Metcalf , Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Andrew Morton , Rik van Riel , Tejun Heo , Thomas Gleixner , Frederic Weisbecker , "Paul E. McKenney" , Christoph Lameter , "Srivatsa S. Bhat" , linux-doc@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/6] nohz: support PR_DATAPLANE_QUIESCE Message-ID: <20150512095030.GD11477@gmail.com> References: <1431107927-13998-1-git-send-email-cmetcalf@ezchip.com> <1431107927-13998-5-git-send-email-cmetcalf@ezchip.com> <20150512093349.GH21418@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150512093349.GH21418@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra wrote: > On Fri, May 08, 2015 at 01:58:45PM -0400, Chris Metcalf wrote: > > This prctl() flag for PR_SET_DATAPLANE sets a mode that requires the > > kernel to quiesce any pending timer interrupts prior to returning > > to userspace. When running with this mode set, sys calls (and page > > faults, etc.) can be inordinately slow. However, user applications > > that want to guarantee that no unexpected interrupts will occur > > (even if they call into the kernel) can set this flag to guarantee > > that semantics. > > Currently people hot-unplug and hot-plug the CPU to do this. > Obviously that's a wee bit horrible :-) > > Not sure if a prctl like this is any better though. This is a CPU > properly not a process one. So if then a prctl() (or other system call) could be a shortcut to: - move the task to an isolated CPU - make sure there _is_ such an isolated domain available I.e. have some programmatic, kernel provided way for an application to be sure it's running in the right environment. Relying on random administration flags here and there won't cut it. Thanks, Ingo From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 4/6] nohz: support PR_DATAPLANE_QUIESCE Date: Tue, 12 May 2015 11:50:30 +0200 Message-ID: <20150512095030.GD11477@gmail.com> References: <1431107927-13998-1-git-send-email-cmetcalf@ezchip.com> <1431107927-13998-5-git-send-email-cmetcalf@ezchip.com> <20150512093349.GH21418@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150512093349.GH21418-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Peter Zijlstra Cc: Chris Metcalf , Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Andrew Morton , Rik van Riel , Tejun Heo , Thomas Gleixner , Frederic Weisbecker , "Paul E. McKenney" , Christoph Lameter , "Srivatsa S. Bhat" , linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org * Peter Zijlstra wrote: > On Fri, May 08, 2015 at 01:58:45PM -0400, Chris Metcalf wrote: > > This prctl() flag for PR_SET_DATAPLANE sets a mode that requires the > > kernel to quiesce any pending timer interrupts prior to returning > > to userspace. When running with this mode set, sys calls (and page > > faults, etc.) can be inordinately slow. However, user applications > > that want to guarantee that no unexpected interrupts will occur > > (even if they call into the kernel) can set this flag to guarantee > > that semantics. > > Currently people hot-unplug and hot-plug the CPU to do this. > Obviously that's a wee bit horrible :-) > > Not sure if a prctl like this is any better though. This is a CPU > properly not a process one. So if then a prctl() (or other system call) could be a shortcut to: - move the task to an isolated CPU - make sure there _is_ such an isolated domain available I.e. have some programmatic, kernel provided way for an application to be sure it's running in the right environment. Relying on random administration flags here and there won't cut it. Thanks, Ingo