Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261642AbVAXUnK (ORCPT ); Mon, 24 Jan 2005 15:43:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261638AbVAXUmI (ORCPT ); Mon, 24 Jan 2005 15:42:08 -0500 Received: from stat16.steeleye.com ([209.192.50.48]:21385 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S261622AbVAXUhN (ORCPT ); Mon, 24 Jan 2005 15:37:13 -0500 Subject: Re: [PATCH] Avoiding fragmentation through different allocator From: James Bottomley To: Marcelo Tosatti Cc: Mel Gorman , William Lee Irwin III , Linux Memory Management List , Linux Kernel , Grant Grundler In-Reply-To: <20050124154927.GJ5925@logos.cnet> References: <20050120101300.26FA5E598@skynet.csn.ul.ie> <20050121142854.GH19973@logos.cnet> <20050122215949.GD26391@logos.cnet> <20050124122952.GA5739@logos.cnet> <1106585052.5513.26.camel@mulgrave> <20050124154927.GJ5925@logos.cnet> Content-Type: text/plain Date: Mon, 24 Jan 2005 14:36:09 -0600 Message-Id: <1106598969.5513.43.camel@mulgrave> Mime-Version: 1.0 X-Mailer: Evolution 2.0.2 (2.0.2-3) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1207 Lines: 26 On Mon, 2005-01-24 at 13:49 -0200, Marcelo Tosatti wrote: > So is it valid to affirm that on average an operation with one SG element pointing to a 1MB > region is similar in speed to an operation with 16 SG elements each pointing to a 64K > region due to the efficient onboard SG processing? it's within a few percent, yes. And the figures depend on how good the I/O card is at it. I can imagine there are some wildly varying I/O cards out there. However, also remember that 1MB of I/O is getting beyond what's sensible for a disc device anyway. The cable speed is much faster than the platter speed, so the device takes the I/O into its cache as it services it. If you overrun the cache it will burp (disconnect) and force a reconnection to get the rest (effectively splitting the I/O up anyway). This doesn't apply to arrays with huge caches, but it does to pretty much everything else. The average disc cache size is only a megabyte or so. James - 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/