From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756540Ab0BRKI6 (ORCPT ); Thu, 18 Feb 2010 05:08:58 -0500 Received: from one.firstfloor.org ([213.235.205.2]:60263 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755992Ab0BRKI4 (ORCPT ); Thu, 18 Feb 2010 05:08:56 -0500 Date: Thu, 18 Feb 2010 11:08:49 +0100 From: Andi Kleen To: Anton Blanchard Cc: Andi Kleen , arun@linux.vnet.ibm.com, tglx@linutronix.de, davem@davemloft.net, linux-kernel@vger.kernel.org, arjan@infradead.org, venkatesh.pallipadi@intel.com Subject: Re: NO_HZ migration of TCP ack timers Message-ID: <20100218100849.GD5964@basil.fritz.box> References: <20100218052820.GD24270@kryten> <87mxz755ks.fsf@basil.nowhere.org> <20100218095529.GA31681@kryten> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100218095529.GA31681@kryten> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 18, 2010 at 08:55:30PM +1100, Anton Blanchard wrote: > > Hi Andi, > > > If the nohz balancer CPU is otherwise idle, shouldn't it have enough > > cycles to handle acks for everyone? Is the problem the cache line > > transfer time? > > Yeah, I think the timer spinlock on the nohz balancer cpu ends up being a > global lock for every other cpu trying to migrate their ack timers to it. And they do that often for short idle periods? For longer idle periods that should be not too bad. -Andi -- ak@linux.intel.com -- Speaking for myself only.