From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756021AbbAPD1U (ORCPT ); Thu, 15 Jan 2015 22:27:20 -0500 Received: from resqmta-po-02v.sys.comcast.net ([96.114.154.161]:35410 "EHLO resqmta-po-02v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752781AbbAPD1S (ORCPT ); Thu, 15 Jan 2015 22:27:18 -0500 Date: Thu, 15 Jan 2015 21:27:14 -0600 (CST) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Steven Rostedt cc: Andrew Morton , Joonsoo Kim , Pekka Enberg , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jesper Dangaard Brouer , Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH v2 1/2] mm/slub: optimize alloc/free fastpath by removing preemption on/off In-Reply-To: <20150115203045.00e9fb73@grimm.local.home> Message-ID: References: <1421307633-24045-1-git-send-email-iamjoonsoo.kim@lge.com> <20150115171634.685237a4.akpm@linux-foundation.org> <20150115203045.00e9fb73@grimm.local.home> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 15 Jan 2015, Steven Rostedt wrote: > profiling function tracing I discovered that accessing preempt_count > was actually quite expensive, even just to read. But it may not be as > bad since Peter Zijlstra converted preempt_count to a per_cpu variable. > Although, IIRC, the perf profiling showed the access to the %gs > register was where the time consuming was happening, which is what > I believe per_cpu variables still use. The %gs register is not used since the address of the per cpu area is available as one of the first fields in the per cpu areas.