Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751818AbaJIR2s (ORCPT ); Thu, 9 Oct 2014 13:28:48 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:37878 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298AbaJIR2j (ORCPT ); Thu, 9 Oct 2014 13:28:39 -0400 Date: Thu, 9 Oct 2014 19:28:34 +0200 From: Peter Zijlstra To: Oleg Nesterov Cc: Kirill Tkhai , Ingo Molnar , Steven Rostedt , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] sched: schedule_tail() should disable preemption Message-ID: <20141009172834.GZ10832@worktop.programming.kicks-ass.net> References: <20141007195046.GA28002@redhat.com> <20141008080016.GB10832@worktop.programming.kicks-ass.net> <20141008183302.GA17495@redhat.com> <20141008183326.GB17495@redhat.com> <20141008193644.GA32055@redhat.com> <1412804248.24248.1.camel@yandex.ru> <20141009145726.GA5604@redhat.com> <20141009151730.GW10832@worktop.programming.kicks-ass.net> <20141009165713.GA13118@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141009165713.GA13118@redhat.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 09, 2014 at 06:57:13PM +0200, Oleg Nesterov wrote: > > Your earlier proposal would penalize every > > !x86 arch by adding extra code to the scheduler core while they already > > automagically preserve their thread_info::preempt_count. > > Sure, and it can't be even compiled on !x86. > > But this is simple, just we need a new helper, preempt_count_restore(), > defined as nop in asm-generic/preempt.h. Well, perhaps another helper > makes sense, preempt_count_raw() which simply reads the counter, but > this is minor. > > After the patch below we can remove ->saved_preempt_count. Including > init_task_preempt_count(), it is no longer needed after the change in > schedule_tail(). Ah, right, this makes more sense. > @@ -2333,10 +2336,12 @@ context_switch(struct rq *rq, struct task_struct *prev, > #endif > > context_tracking_task_switch(prev, next); > + > + pc = preempt_count(); The only problem here is that you can loose PREEMPT_NEED_RESCHED, I haven't thought about whether that is a problem here or not. > /* Here we just switch the register state and the stack. */ > switch_to(prev, next, prev); > - > barrier(); > + preempt_count_restore(pc); > /* > * this_rq must be evaluated again because prev may have moved > * CPUs since it called schedule(), thus the 'rq' on its stack > -- 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/