From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751747Ab1IZHgv (ORCPT ); Mon, 26 Sep 2011 03:36:51 -0400 Received: from merlin.infradead.org ([205.233.59.134]:42714 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750808Ab1IZHgu convert rfc822-to-8bit (ORCPT ); Mon, 26 Sep 2011 03:36:50 -0400 Subject: Re: [PATCH 5/5] slub: Only IPI CPUs that have per cpu obj to flush From: Peter Zijlstra To: Pekka Enberg Cc: Gilad Ben-Yossef , linux-kernel@vger.kernel.org, Frederic Weisbecker , Russell King , Chris Metcalf , linux-mm@kvack.org, Christoph Lameter , Matt Mackall Date: Mon, 26 Sep 2011 09:36:05 +0200 In-Reply-To: References: <1316940890-24138-1-git-send-email-gilad@benyossef.com> <1316940890-24138-6-git-send-email-gilad@benyossef.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.3- Message-ID: <1317022565.9084.60.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2011-09-26 at 09:54 +0300, Pekka Enberg wrote: > > AFAICT, flush_all() isn't all that performance sensitive. Why do we > want to reduce IPIs here? Because it can wake up otherwise idle CPUs, wasting power. Or for the case I care more about, unnecessarily perturb a CPU that didn't actually have anything to flush but was running something, introducing jitter. on_each_cpu() things are bad when you have a ton of CPUs (which is pretty normal these days).