From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751865AbbCQF4y (ORCPT ); Tue, 17 Mar 2015 01:56:54 -0400 Received: from resqmta-ch2-07v.sys.comcast.net ([69.252.207.39]:48551 "EHLO resqmta-ch2-07v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751292AbbCQF4x (ORCPT ); Tue, 17 Mar 2015 01:56:53 -0400 Date: Tue, 17 Mar 2015 00:56:51 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Steven Rostedt cc: LKML , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , =?ISO-8859-15?Q?Uwe_Kleine-K=F6nig?= , linux-arm-kernel@lists.infradead.org, Russell King Subject: Re: [RFC][PATCH] ring-buffer: Replace this_cpu_{read,write} with this_cpu_ptr() In-Reply-To: <20150316173154.537b80ee@gandalf.local.home> Message-ID: References: <20150316173154.537b80ee@gandalf.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 Mon, 16 Mar 2015, Steven Rostedt wrote: > It has come to my attention that this_cpu_read/write are horrible on > architectures other than x86. Worse yet, they actually disable > preemption or interrupts! This caused some unexpected tracing results > on ARM. Well its just been 7 years or so. Took a long time it seems. These would need to be implemented on the architectures to have comparable performance. > I may go and remove all this_cpu_read,write() calls from my code > because of this. You could do that with __this_cpo_* but not this_cpu_*(). Doing it to this_cpu_* would make the operations no longer per cpu atomic. If they do not need per cpu atomicity then you could have used __this_cpu_* instead. And __this_cpu_* do not disable preemption or interrupts. So please do not send patches based on gut reactions. NAK