Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756087AbYKGXhU (ORCPT ); Fri, 7 Nov 2008 18:37:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753738AbYKGX3X (ORCPT ); Fri, 7 Nov 2008 18:29:23 -0500 Received: from mx2.redhat.com ([66.187.237.31]:55867 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755377AbYKGX3W (ORCPT ); Fri, 7 Nov 2008 18:29:22 -0500 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20081107171703.GE22134@Krystal> References: <20081107171703.GE22134@Krystal> <20081107164758.GB22134@Krystal> <20081107003816.9b0f947a.akpm@linux-foundation.org> <20081107052336.652868737@polymtl.ca> <20081107053349.861709786@polymtl.ca> <20081106220530.5b0e3a96.akpm@linux-foundation.org> <25363.1226056819@redhat.com> <8481.1226077497@redhat.com> To: Mathieu Desnoyers Cc: dhowells@redhat.com, Andrew Morton , Nicolas Pitre , Linus Torvalds , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, Ralf Baechle , benh@kernel.crashing.org, paulus@samba.org, David Miller , Ingo Molnar , Thomas Gleixner , Steven Rostedt , linux-arch@vger.kernel.org Subject: Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb() Date: Fri, 07 Nov 2008 23:27:59 +0000 Message-ID: <9302.1226100479@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 976 Lines: 23 Mathieu Desnoyers wrote: > Yes. Do you think the synchronization of the cycles counters is > _perfect_ across CPUs so that there is no possible way whatsoever that > two cycle counter values appear to go backward between CPUs ? (also > taking in account delays in __m_cnt_hi write-back...) Given there's currently only one CPU allowed, yes, I think it's perfect:-) It's something to re-evaluate should Panasonic decide to do SMP. > If we expect the only correct use-case to be with readl(), I don't see > the problem with added synchronization. It might be expensive if you don't actually want to call readl(). But that's on a par with using funky instructions to read the TSC, I guess. David -- 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/