From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 4/6] nohz: support PR_DATAPLANE_QUIESCE Date: Tue, 12 May 2015 11:33:49 +0200 Message-ID: <20150512093349.GH21418@twins.programming.kicks-ass.net> References: <1431107927-13998-1-git-send-email-cmetcalf@ezchip.com> <1431107927-13998-5-git-send-email-cmetcalf@ezchip.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1431107927-13998-5-git-send-email-cmetcalf-d5a29ZRxExrQT0dZR+AlfA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Chris Metcalf Cc: 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 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. ISTR people talking about 'quiesce' sysfs file, along side the hotplug stuff, I can't quite remember.