From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: AHCI_MAX_SG Date: Sat, 20 Aug 2005 02:45:21 -0400 Message-ID: <4306D181.5050205@pobox.com> References: <20050609090859.GO5140@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail.dvmed.net ([216.237.124.58]:10721 "EHLO mail.dvmed.net") by vger.kernel.org with ESMTP id S1751078AbVHTGp1 (ORCPT ); Sat, 20 Aug 2005 02:45:27 -0400 In-Reply-To: <20050609090859.GO5140@suse.de> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Jens Axboe , "linux-ide@vger.kernel.org" Jens Axboe wrote: > Been wondering about this weird value for a while - why does it default > to 168 segments? As clustering is disabled, that makes 672KiB the > largest supported request. So currently the dma mapped controller > command area is about 91KiB in size, I guess the limit is meant to limit > the size of that area because 256 would be nicer. So how about making it > 160 which makes the resulting command at least a multiple of 128, or > even just 128 which gives us a nice clean 512KiB? (I hope you don't mind me making a private message public -- several people have asked this, and even you have brought this up in public) 168 is the number that guarantees that AHCI_PORT_PRIV_DMA_SZ is 4K. No other reason, and, it can (and probably will) be increased in the future. Jeff