Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263620AbTE0OH1 (ORCPT ); Tue, 27 May 2003 10:07:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263624AbTE0OH1 (ORCPT ); Tue, 27 May 2003 10:07:27 -0400 Received: from nat9.steeleye.com ([65.114.3.137]:46852 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S263620AbTE0OH0 (ORCPT ); Tue, 27 May 2003 10:07:26 -0400 Subject: Re: [BK PATCHES] add ata scsi driver From: James Bottomley To: Jens Axboe Cc: Linus Torvalds , Linux Kernel In-Reply-To: <20030527065436.GX845@suse.de> References: <20030526205725.GT845@suse.de> <20030527065436.GX845@suse.de> Content-Type: text/plain Content-Transfer-Encoding: 7bit X-Mailer: Ximian Evolution 1.0.8 (1.0.8-9) Date: 27 May 2003 10:20:32 -0400 Message-Id: <1054045236.1974.20.camel@mulgrave> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1549 Lines: 34 On Tue, 2003-05-27 at 02:54, Jens Axboe wrote: > James, speaking of queue localities and tcq... Doug mentioned some time > ago that aic7xxx dishes out tags numbers from a hba pool which makes it > impossible to support with out current block layer queueing code. Maybe > it we associate the blk_queue_tag structure with a bunch of queues > instead of having a 1:1 mapping it could work. Yes, A large number of devices (not just the aic7xxx) have a single issue queue for all outgoing requests (this is the reason for the can_queue limit in the host template). If the issue queue is < 256 slots, it makes a lot of sense to use global tag numbers instead of device local ones, since then you can simply map the returning tag number to an index in the issue queue and not bother having to keep a hash table of to look it up in. Even drivers which have larger or variable size issue queues (here the qlogic ones spring immediately to mind) often have a virtual index number attached to their commands (which, this time is 16 bits) which they'd like to use as a unique offset into the issue queue. Obviously, they face exactly the same challenges as tags and they'd like a similar solution. A global structure for a bunch of queues would probably be the most useful way forwards. 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/