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Subject: RE: [linux-pm] Power management for SCSI
Date: Wed, 13 Aug 2008 16:03:57 -0400
Message-ID: <556445368AFA1C438794ABDA8901891C094876DA@USA0300MS03.na.xerox.net>
In-Reply-To: <Pine.LNX.4.44L0.0808131534440.13982-100000@iolanthe.rowland.org>
Thread-Topic: [linux-pm] Power management for SCSI
Thread-Index: Acj9fgOinRSiEJBfQF+cb9OZZ6kalgAAH0HQ
References: <200808131825.27303.oneukum@suse.de> <Pine.LNX.4.44L0.0808131534440.13982-100000@iolanthe.rowland.org>
From: "Leisner, Martin" <Martin.Leisner@xerox.com>
To: "Alan Stern" <stern@rowland.harvard.edu>,
       "Oliver Neukum" <oneukum@suse.de>
Cc: "Linux-pm mailing list" <linux-pm@lists.osdl.org>,
       "kernel list" <linux-kernel@vger.kernel.org>, <teheo@novell.com>,
       <James.Bottomley@hansenpartnership.com>, "Pavel Machek" <pavel@suse.cz>,
       "Stefan Richter" <stefanr@s5r6.in-berlin.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2740
Lines: 77

Regarding these scsi suspend patches, there's a general
problem to drop power on disk devices on a running system.
I discussed it in:

http://www.gossamer-threads.com/lists/linux/kernel/811598

We have a sequence:
    a) stop further block requests
    b) sync the disk (and sync the cache -- there was talk on and off
       for several years about sync not realling syncing)
    c) drop power on the disk

We tweak the ext3 mount timeout and the /proc/sys/vm settings to put
the computer into laptop mode.

When a read comes along, we reverse the process...(or a forced write
which generally won't happen).

But we need to add patches to the device driver and the block layer to
enable this...it seems useful if there was a more generic way to
handle it...maybe registering a callback to reenable power and a
mechanism
to start the poweroff sequence...

We've done this in 2.6.20, I wonder if there's any work along these
lines in recent kernels (I'm going to look at 2.6.2[67]...)

Marty

>   -----Original Message-----
>   From: linux-pm-bounces@lists.linux-foundation.org [mailto:linux-pm-
>   bounces@lists.linux-foundation.org] On Behalf Of Alan Stern
>   Sent: Wednesday, August 13, 2008 3:37 PM
>   To: Oliver Neukum
>   Cc: Linux-pm mailing list; kernel list; teheo@novell.com;
>   James.Bottomley@hansenpartnership.com; Pavel Machek; Stefan Richter
>   Subject: Re: [linux-pm] Power management for SCSI
>   
>   On Wed, 13 Aug 2008, Oliver Neukum wrote:
>   
>   > > In Alan's patch, SCSI calls scsi_host_template methods (if the
LLD
>   > > provides ones) to suspend and resume a Scsi_Host.  The LLD can
use
>   them
>   > > to work with the underlying infrastructure to determine what can
be
>   done
>   > > at that time.  I.e. are there other protocols or other
initiator-
>   like
>   > > nodes sharing the link?  If yes or if "maybe yes", the
>   infrastructure
>   > > keeps the link up.  If not, it can move it into a low-power
state.
>   >
>   > That is a parculiar way of viewing it. Alan's patch introduce
runtime
>   > pm attributes to the devices. Quoting:
>   >
>   
>   With the original patch, you can't operate on the link independent
from
>   the devices.  But with the revised patch (whenever I manage to find
>   time to write it!), you _will_ be able to.
>   
>   Alan Stern
>   
>   _______________________________________________
>   linux-pm mailing list
>   linux-pm@lists.linux-foundation.org
>   https://lists.linux-foundation.org/mailman/listinfo/linux-pm
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