Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753553AbaG2MHt (ORCPT ); Tue, 29 Jul 2014 08:07:49 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:53287 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753139AbaG2MHs (ORCPT ); Tue, 29 Jul 2014 08:07:48 -0400 Date: Tue, 29 Jul 2014 14:07:39 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: LKML , Ingo Molnar , Nicolas Pitre , "Paul E. McKenney" , Steven Rostedt , Thomas Gleixner , Viresh Kumar Subject: Re: [PATCH 05/10] smp: Fast path check on IPI list Message-ID: <20140729120739.GX3935@laptop> References: <1406569056-30217-1-git-send-email-fweisbec@gmail.com> <1406569056-30217-6-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1406569056-30217-6-git-send-email-fweisbec@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 28, 2014 at 07:37:31PM +0200, Frederic Weisbecker wrote: > When we enqueue a remote irq work, we trigger the same IPI as those > raised by smp_call_function_*() family. > > So when we receive such IPI, we check both irq_work and smp_call_function > queues. Thus if we trigger a remote irq work, we'll likely find the > smp_call_function queue empty unless we collide with concurrent enqueuers > but the probability is low. > > Meanwhile, checking the smp_call_function queue can be costly because > we use llist_del_all() which relies on cmpxchg(). xchg() -- 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/