From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756528AbZCABot (ORCPT ); Sat, 28 Feb 2009 20:44:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755178AbZCABol (ORCPT ); Sat, 28 Feb 2009 20:44:41 -0500 Received: from terminus.zytor.com ([198.137.202.10]:34484 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753666AbZCABok (ORCPT ); Sat, 28 Feb 2009 20:44:40 -0500 Message-ID: <49A9E7A3.4050102@zytor.com> Date: Sat, 28 Feb 2009 17:40:51 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Arjan van de Ven CC: Andi Kleen , David Miller , torvalds@linux-foundation.org, mingo@elte.hu, nickpiggin@yahoo.com.au, sqazi@google.com, linux-kernel@vger.kernel.org, tglx@linutronix.de Subject: Re: [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache() References: <20090228092450.3ded2db5@infradead.org> <20090228.160651.228301019.davem@davemloft.net> <20090301004003.GF26292@one.firstfloor.org> <49A9D6CA.30906@zytor.com> <20090228163811.48b1de72@infradead.org> <20090301014822.GG26292@one.firstfloor.org> <20090228173813.6d86c0ef@infradead.org> In-Reply-To: <20090228173813.6d86c0ef@infradead.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Arjan van de Ven wrote: > > the reason that movntq and co are faster is because you avoid the > write-allocate behavior of the caches.... > > the cache polluting part of it I find hard to buy for general use (as > this discussion shows)... that will be extremely hard to measure as > a real huge thing, while the WA part is like a 1.5x to 2x thing. > Note that hardware *can* (which is not the same thing as hardware *will*) elide the write-allocate behavior. We did that at Transmeta for rep movs and certain other instructions which provably filled in entire cache lines. I haven't investigated if newer Intel CPUs do that in the "fast rep movs" case. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.