Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753585AbbDBTT6 (ORCPT ); Thu, 2 Apr 2015 15:19:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59793 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752217AbbDBTT4 (ORCPT ); Thu, 2 Apr 2015 15:19:56 -0400 Date: Thu, 2 Apr 2015 21:19:35 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Frederic Weisbecker , LKML , Dave Jones , Thomas Gleixner , "Paul E . McKenney" , Ingo Molnar , Rik van Riel Subject: Re: [PATCH 2/3] context_tracking: Inherit TIF_NOHZ through forks instead of context switches Message-ID: <20150402191934.GA24360@redhat.com> References: <1427996365-12101-1-git-send-email-fweisbec@gmail.com> <1427996365-12101-3-git-send-email-fweisbec@gmail.com> <20150402190910.GF27490@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150402190910.GF27490@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1057 Lines: 28 On 04/02, Peter Zijlstra wrote: > > On Thu, Apr 02, 2015 at 07:39:24PM +0200, Frederic Weisbecker wrote: > > TIF_NOHZ is used by context_tracking to force syscall slow-path on every > > task in order to track userspace roundtrips. As such, it must be set on > > all running tasks. > > > > It's currently explicitly inherited through context switches. There is > > no need to do it on this fast-path though. The flag could be simply > > set once for all on all tasks, whether they are running or not. > > > > Lets do this by setting the flag to init task on early boot and let it > > propagate through fork inheritance. > > > > One must ask, what's the point of the flag if everybody must always have > it set? To force the slow path in the syscall paths. Unfortunately it is not easy to change this ... Oleg. -- 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/