Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752135Ab3J2TZO (ORCPT ); Tue, 29 Oct 2013 15:25:14 -0400 Received: from smtpauth05h.mfg.siteprotect.com ([64.26.60.146]:38712 "EHLO smtpauth05.mfg.siteprotect.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751803Ab3J2TZM (ORCPT ); Tue, 29 Oct 2013 15:25:12 -0400 Date: Tue, 29 Oct 2013 15:27:05 -0400 (EDT) From: Vince Weaver X-X-Sender: vince@pianoman.cluster.toy To: Peter Zijlstra cc: Victor Kaplansky , Oleg Nesterov , Anton Blanchard , Benjamin Herrenschmidt , Frederic Weisbecker , LKML , Linux PPC dev , Mathieu Desnoyers , Michael Ellerman , Michael Neuling , "Paul E. McKenney" Subject: Re: perf events ring buffer memory barrier on powerpc In-Reply-To: <20131029103057.GN2490@laptop.programming.kicks-ass.net> Message-ID: References: <12083.1382486094@ale.ozlabs.ibm.com> <20131023141948.GB3566@localhost.localdomain> <20131025173749.GG19466@laptop.lan> <20131028132634.GO19466@laptop.lan> <20131028163418.GD4126@linux.vnet.ibm.com> <20131028201735.GA15629@redhat.com> <20131029102131.GA16117@laptop.programming.kicks-ass.net> <20131029103057.GN2490@laptop.programming.kicks-ass.net> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-CTCH-Spam: Unknown X-CTCH-RefID: str=0001.0A020207.52700B97.00D0,ss=1,re=0.100,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1182 Lines: 29 On Tue, 29 Oct 2013, Peter Zijlstra wrote: > On Tue, Oct 29, 2013 at 11:21:31AM +0100, Peter Zijlstra wrote: > --- linux-2.6.orig/include/uapi/linux/perf_event.h > +++ linux-2.6/include/uapi/linux/perf_event.h > @@ -479,13 +479,15 @@ struct perf_event_mmap_page { > /* > * Control data for the mmap() data buffer. > * > - * User-space reading the @data_head value should issue an rmb(), on > - * SMP capable platforms, after reading this value -- see > - * perf_event_wakeup(). > + * User-space reading the @data_head value should issue an smp_rmb(), > + * after reading this value. so where's the patch fixing perf to use the new recommendations? Is this purely a performance thing or a correctness change? A change like this a bit of a pain, especially as userspace doesn't really have nice access to smb_mb() defines so a lot of cut-and-pasting will ensue for everyone who's trying to parse the mmap buffer. Vince -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/