Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756936AbYGNXQn (ORCPT ); Mon, 14 Jul 2008 19:16:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759274AbYGNXQd (ORCPT ); Mon, 14 Jul 2008 19:16:33 -0400 Received: from mx1.redhat.com ([66.187.233.31]:47741 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758947AbYGNXQc (ORCPT ); Mon, 14 Jul 2008 19:16:32 -0400 Date: Mon, 14 Jul 2008 19:16:17 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@devserv.devel.redhat.com To: David Miller cc: andi@firstfloor.org, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, jens.axboe@oracle.com Subject: Re: [SUGGESTION]: drop virtual merge accounting in I/O requests In-Reply-To: <20080714.143751.266098047.davem@davemloft.net> Message-ID: References: <20080714.052859.88212003.davem@davemloft.net> <20080714.143751.266098047.davem@davemloft.net> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1256 Lines: 29 >>>> As you mentioned ESP driver, it declares .sg_tablesize = SG_ALL, so >>>> BIO_VMERGE_BOUNDARY has no effect on the operation of this driver. Any >>>> other driver where BIO_VMERGE_BOUNDARY does matter? >>> >>> When BIO_VMERGE_BOUNDARY is turned on, requests that would not >>> otherwise fit into the device's limits, can. >> >> Why would someone want to overshoot SG_ALL? ... and, shouldn't the >> constant be increased then --- instead of making buggy BIO_VMERGE_BOUNDARY >> expectations? > > I'm talking about other devices, not about the ESP, here. And which ones are those important drivers that need merge accounting? A100U2W is an old card, I got it for $8.5 in bazaar, it does 38MB/s. This virtual merge accounting helps to stuff on average 4 more segments into the 32-entry table. So the question is: to reduce number of requests by 12% on an outdated SCSI card, it is sensible to maintain complicated merge accounting logic in the core block layer? To me, it doesn't seem sensible. Mikulas -- 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/