From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: SCSI dynamic power management Date: Wed, 21 Nov 2007 13:56:44 +0100 Message-ID: <20071121125643.GN6956@kernel.dk> References: <20071119154650.GC12494@parisc-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from brick.kernel.dk ([87.55.233.238]:20019 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751897AbXKUM7r (ORCPT ); Wed, 21 Nov 2007 07:59:47 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Alan Stern Cc: Matthew Wilcox , Oliver Neukum , SCSI development list On Mon, Nov 19 2007, Alan Stern wrote: > On Mon, 19 Nov 2007, Matthew Wilcox wrote: > > > On Mon, Nov 19, 2007 at 10:36:19AM -0500, Alan Stern wrote: > > > These are conflicting requirements. How can we send the START-STOP > > > UNIT commands to spin the disk up/down through the request queue while > > > delaying or failing all others? > > > > You can insert commands at the head of a request queue. > > Sure. But that won't do any good if the requests get held on the queue > (or failed immediately) because the disk is supposedly "suspended". > Somehow those requests have to be allowed to proceed while all others > are forced to wait (or to fail). Yeah, head-of-queue or not has no relevance. But the SCSI layer has had the notion of 'allow some commands, disallow others' for quite some time already - grep for REQ_PREEMPT in scsi/ -- Jens Axboe