From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <42C17028.6050903@yahoo.com.au> Date: Wed, 29 Jun 2005 01:43:36 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [patch 2] mm: speculative get_page References: <42C0AAF8.5090700@yahoo.com.au> <20050628040608.GQ3334@holomorphy.com> <42C0D717.2080100@yahoo.com.au> <20050627.220827.21920197.davem@davemloft.net> <20050628141903.GR3334@holomorphy.com> In-Reply-To: <20050628141903.GR3334@holomorphy.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: William Lee Irwin III Cc: "David S. Miller" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Anton Blanchard List-ID: William Lee Irwin III wrote: > On Mon, Jun 27, 2005 at 10:08:27PM -0700, David S. Miller wrote: > >>BTW, I disagree with this assertion. spin_unlock() does imply a >>memory barrier. >>All memory operations before the release of the lock must execute >>before the lock release memory operation is globally visible. > > > The affected architectures have only recently changed in this regard. > ppc64 was the most notable case, where it had a barrier for MMIO > (eieio) but not a general memory barrier. PA-RISC likewise formerly had > no such barrier and was a more normal case, with no barrier whatsoever. > > Both have since been altered, ppc64 acquiring a heavyweight sync > (arch nomenclature), and PA-RISC acquiring 2 memory barriers. > Parisc looks like it's doing the extra memory barrier to "be safe" :P Re the ppc64 chageset: It looks to me like lwsync is the lightweight sync, and eieio is just referred to as the lightER (than sync) weight sync. What's more, it looks like eieio does order stores to system memory and is not just an MMIO barrier. But nit picking aside, is it true that we need a load barrier before unlock? (store barrier I agree with) The ppc64 changeset in question indicates yes, but I can't quite work out why. There are noises in the archives about this, but I didn't pinpoint a conclusion... Send instant messages to your online friends http://au.messenger.yahoo.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org