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

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Date:	Wed, 08 Aug 2007 10:24:25 -0400
From:	Mark Lord <lkml@....ca>
To:	Tejun Heo <htejun@...il.com>
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

Tejun Heo wrote:
> Mark Lord wrote:
>> > Tejun Heo wrote:
>>> >> Michael Sedkowski wrote:
>>>> >>> Dnia 07-08-2007, Wt o godzinie 03:43 +0900, Tejun Heo napisaÅ‚(a):
>>>>> >>>> Does emergency unload count increase
>>>>> >>>> after each power down? 
>>>> >>> I think I got it.
>>>> >>> Using smartctl I've done a test and shut down, then repeted the test.
>>>> >>> The only values that where diffrent are temperatures and
>>>> >>> Hardware_ECC_Recovered which rised by 6 points.
>>>> >>> However I have no idea which of those is the "emergency count"...
>>>> >>> Full results in attachment.
>>>> >>>
>>>> >>> 192 Power-Off_Retract_Count 0x0032   100   100   000    Old_age  
>>>> >>> Always       -       388
>>> >>
>>> >> I think this is the one.  You can test it by forcefully powering off the
>>> >> machine (press power button for several secs or disconnect AC and
>>> >> battery) and see whether the count increases.
>> > 
>> > FWIW, Tejun, with 2.6.22, my new Seagate 160GB SATA drive (notebook)
>> > increments the "Power-Off_Retract_Count" on each suspend-to-RAM operation.
>> > It does not do any double spin-up/spin-down things though.
>> > 
>> > What a mess.
> 
> Hmmm.. It shouldn't.  libata now issues STANDBYNOW prior to entering
> STR.  Can you instrument code a bit and see whether it actually gets issued?

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.
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