Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261904AbTICLUR (ORCPT ); Wed, 3 Sep 2003 07:20:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261960AbTICLUR (ORCPT ); Wed, 3 Sep 2003 07:20:17 -0400 Received: from smtp.bitmover.com ([192.132.92.12]:60616 "EHLO smtp.bitmover.com") by vger.kernel.org with ESMTP id S261904AbTICLUL (ORCPT ); Wed, 3 Sep 2003 07:20:11 -0400 Date: Wed, 3 Sep 2003 04:19:34 -0700 From: Larry McVoy To: "Brown, Len" Cc: Giuliano Pochini , Larry McVoy , linux-kernel@vger.kernel.org Subject: Re: Scaling noise Message-ID: <20030903111934.GF10257@work.bitmover.com> Mail-Followup-To: Larry McVoy , "Brown, Len" , Giuliano Pochini , Larry McVoy , linux-kernel@vger.kernel.org References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4i X-MailScanner-Information: Please contact the ISP for more information X-MailScanner: Found to be clean X-MailScanner-SpamCheck: not spam (whitelisted), SpamAssassin (score=0.5, required 7, AWL, DATE_IN_PAST_06_12) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1148 Lines: 28 On Wed, Sep 03, 2003 at 05:41:39AM -0400, Brown, Len wrote: > > Latency is not bandwidth. > > Bingo. > > The way to address memory latency is by increasing bandwidth and > increasing parallelism to use it -- thus amortizing the latency. And if the app is a pointer chasing app, as many apps are, that doesn't help at all. It's pretty much analogous to file systems. If bandwidth was the answer then we'd all be seeing data moving at 60MB/sec off the disk. Instead we see about 4 or 5MB/sec. Expecting more bandwidth to help your app is like expecting more platter speed to help your file system. It's not the platter speed, it's the seeks which are the problem. Same thing in system doesn't, it's not the bcopy speed, it's the cache misses that are the problem. More bandwidth doesn't do much for that. -- --- Larry McVoy lm at bitmover.com http://www.bitmover.com/lm - 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/