From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753279AbbCQMNp (ORCPT ); Tue, 17 Mar 2015 08:13:45 -0400 Received: from smtprelay0219.hostedemail.com ([216.40.44.219]:43607 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752111AbbCQMNo (ORCPT ); Tue, 17 Mar 2015 08:13:44 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:968:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2198:2199:2393:2553:2559:2562:2893:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3872:3873:3874:4250:5007:6119:6261:7875:7903:8784:9040:10004:10400:10848:10967:11026:11232:11658:11914:12114:12517:12519:12740:13069:13161:13221:13229:13311:13357:14096:14097:21080:21088,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: spark20_3d81abb6d1b43 X-Filterd-Recvd-Size: 2477 Date: Tue, 17 Mar 2015 08:13:41 -0400 From: Steven Rostedt To: Christoph Lameter Cc: LKML , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Uwe =?UTF-8?B?S2xlaW5lLUvDtm5pZw==?= , linux-arm-kernel@lists.infradead.org, Russell King Subject: Re: [RFC][PATCH] ring-buffer: Replace this_cpu_{read,write} with this_cpu_ptr() Message-ID: <20150317081341.0f9a8b4c@gandalf.local.home> In-Reply-To: References: <20150316173154.537b80ee@gandalf.local.home> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 17 Mar 2015 00:56:51 -0500 (CDT) Christoph Lameter wrote: > 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. The code that I added was not 7 years old. And not all people send me reports like this. > > 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. I do not need it to be atomic. > > So please do not send patches based on gut reactions. What else would you like me to do? It was an RFC, and it worked. > > NAK For this particular patch, I may override the NAK as I do not see a downside for it. Why should x86 get an advantage at the expense of ARM? -- Steve