From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Howells 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> 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> Return-path: 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 In-Reply-To: <20081107171703.GE22134@Krystal> Sender: linux-arch-owner@vger.kernel.org List-ID: 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 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