linux-kernel - Re: Disk spin down issue on shut down/suspend to disk

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Date:	Wed, 08 Aug 2007 23:30:18 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Mark Lord <lkml@....ca>
CC:	Michael Sedkowski <sedmich@...il.com>, trenn@...e.de,
	Robert Hancock <hancockr@...w.ca>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: Disk spin down issue on shut down/suspend to disk

Mark Lord wrote:
> Heh.. I haven't instrumented it yet, but I did discover a bit more about
> it:
> 
> The Power-Off_Retract_Count incrmenents *only* when there's data in the
> on-drive write-cache.  So if I haven't written anything significantly large
> before suspending, then it often does NOT increment the retract counter.
> 
> But if I copy a couple of multi-MB files around and then suspend (to RAM),
> the retract count gets incremented.
> 
> So I've now just stuck "hdparm -F /dev/sda" into my suspend script,
> and that cures the problem completely for me.  "-F" does a FLUSH_CACHE,
> and requires a recent copy of hdparm.
> 
> Perhaps libata should also do a FLUSH_CACHE before any STANDBYNOW command,
> prior to entering STR, which is what my script is currently now doing..
> 
> I'll instrument libata and see what the current sequence is.

Hmmmm.. libata should issue FLUSH CACHE on STR too.  sd_suspend() and
sd_shutdown() are pretty similar after all.

-- 
tejun
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