Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262853AbUKTDWr (ORCPT ); Fri, 19 Nov 2004 22:22:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263071AbUKTDQL (ORCPT ); Fri, 19 Nov 2004 22:16:11 -0500 Received: from smtp205.mail.sc5.yahoo.com ([216.136.129.95]:46931 "HELO smtp205.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S262853AbUKTDOj (ORCPT ); Fri, 19 Nov 2004 22:14:39 -0500 Message-ID: <419EB699.4050204@yahoo.com.au> Date: Sat, 20 Nov 2004 14:14:33 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040820 Debian/1.7.2-4 X-Accept-Language: en MIME-Version: 1.0 To: William Lee Irwin III CC: Christoph Lameter , torvalds@osdl.org, akpm@osdl.org, Benjamin Herrenschmidt , Hugh Dickins , linux-mm@kvack.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, Robin Holt Subject: Re: page fault scalability patch V11 [0/7]: overview References: <419D581F.2080302@yahoo.com.au> <419D5E09.20805@yahoo.com.au> <1100848068.25520.49.camel@gaston> <20041120020401.GC2714@holomorphy.com> <419EA96E.9030206@yahoo.com.au> <20041120023443.GD2714@holomorphy.com> <419EAEA8.2060204@yahoo.com.au> <20041120030425.GF2714@holomorphy.com> In-Reply-To: <20041120030425.GF2714@holomorphy.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2178 Lines: 63 William Lee Irwin III wrote: > William Lee Irwin III wrote: > >>>Furthermore, see Robin Holt's results regarding the performance of the >>>atomic operations and their relation to cacheline sharing. > > > On Sat, Nov 20, 2004 at 01:40:40PM +1100, Nick Piggin wrote: > >>Well yeah, but a. their patch isn't in 2.6 (or 2.4), and b. anon_rss > > > Irrelevant. Unshare cachelines with hot mm-global ones, and the > "problem" goes away. > That's the idea. > This stuff is going on and on about some purist "no atomic operations > anywhere" weirdness even though killing the last atomic operation > creates problems and doesn't improve performance. > Huh? How is not wanting to impact single threaded performance being "purist weirdness"? Practical, I'd call it. > > On Sat, Nov 20, 2004 at 01:40:40PM +1100, Nick Piggin wrote: > >>means another atomic op. While this doesn't immediately make it a >>showstopper, it is gradually slowing down the single threaded page >>fault path too, which is bad. > > > William Lee Irwin III wrote: > >>>And frankly, the argument that the space overhead of per-cpu counters >>>is problematic is not compelling. Even at 1024 cpus it's smaller than >>>an ia64 pagetable page, of which there are numerous instances attached >>>to each mm. > > > On Sat, Nov 20, 2004 at 01:40:40PM +1100, Nick Piggin wrote: > >>1024 CPUs * 64 byte cachelines == 64K, no? Well I'm sure they probably >>don't even care about 64K on their large machines, but... >>On i386 this would be maybe 32 * 128 byte == 4K per task for distro >>kernels. Not so good. > > > Why the Hell would you bother giving each cpu a separate cacheline? > The odds of bouncing significantly merely amongst the counters are not > particularly high. > Hmm yeah I guess wouldn't put them all on different cachelines. As you can see though, Christoph ran into a wall at 8 CPUs, so having them densly packed still might not be enough. - 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/