From: Jens Axboe <jens.axboe@oracle.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Matthew Wilcox <matthew@wil.cx>,
Oliver Neukum <oliver@neukum.name>,
SCSI development list <linux-scsi@vger.kernel.org>
Subject: Re: SCSI dynamic power management
Date: Wed, 21 Nov 2007 13:56:44 +0100 [thread overview]
Message-ID: <20071121125643.GN6956@kernel.dk> (raw)
In-Reply-To: <Pine.LNX.4.44L0.0711191054360.4806-100000@iolanthe.rowland.org>
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
next prev parent reply other threads:[~2007-11-21 12:59 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-19 15:36 SCSI dynamic power management Alan Stern
2007-11-19 15:46 ` Matthew Wilcox
2007-11-19 15:57 ` Alan Stern
2007-11-19 16:14 ` Salyzyn, Mark
2007-11-19 16:46 ` Alan Stern
2007-11-19 16:53 ` James Bottomley
2007-11-19 19:16 ` Alan Stern
2007-11-19 19:18 ` Matthew Wilcox
2007-11-19 19:48 ` Alan Stern
2007-11-20 14:53 ` James Bottomley
2007-11-20 15:07 ` Oliver Neukum
2007-11-20 15:21 ` James Bottomley
2007-11-20 15:36 ` Oliver Neukum
2007-11-20 15:42 ` James Bottomley
2007-11-20 16:02 ` Alan Stern
2007-11-20 16:15 ` James Bottomley
2007-11-20 19:03 ` Alan Stern
2007-11-21 12:56 ` Jens Axboe [this message]
2007-11-20 14:38 ` Douglas Gilbert
2007-11-20 15:49 ` Alan Stern
[not found] <4741AFEA.8000408@emulex.com>
2007-11-19 16:00 ` Alan Stern
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