linux-kernel - Re: 2.6.18-rc2, problem to wake up spinned down drive?

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Date:	Tue, 08 Aug 2006 14:40:15 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Tejun Heo <htejun@...il.com>
CC:	Harald Dunkel <harald.dunkel@...nline.de>,
	Pavel Machek <pavel@....cz>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.18-rc2, problem to wake up spinned down drive?

Tejun Heo wrote:

> Harald Dunkel wrote:
>
>> Tejun Heo wrote:
>>
>>> Pavel Machek wrote:
>>>
>>>>> echo 1 > /sys/bus/scsi/devices/1:0:0:0/power/state
>>>>
>>>> Really? I thought power/state takes 0/3 (for D0 and D3)
>>>
>>> Yes, of course.  My mistake.  Sorry about the confusion.  The correct
>>> command is 'echo -n 3 > /sys/bus/scsi/devices/x:y:z:w/power/state'.
>>>
>>
>> (Sure?  :-)
>
>
> The sleeping part is correct.  That will make libata put the disk to 
> sleep.
>
>> Now this did not work at all. The '-n 3' was probably
>> correct, but when I tried to access the disk, then it
>> did not spin up again (I waited for 5 minutes). There
>> was no message on the console, either.
>>
>> But I could not reproduce this problem.
>>
>> How do I monitor that the disk spins down and up?
>
>
> But the waking up part isn't.  You need to issue wake up explicitly by 
> doing 'echo -n 0 > /sys/...'  I've been a complete idiot in this 
> thread.  Please excuse me.  :-(
>
> I think the solution to your problem is adjusting command timeout to 
> more reasonable values which should make the problem more bearable. 
> It'll take some time to figure out how to make timeouts more 
> intelligent without breaking support for slow devices.  I'll work on 
> that. 

Tejun, would it be possible and sensible to either let the user tune 
this per-drive, or to have the kernel note how long {something} takes 
and auto-tune to that? As you said, the issue is not breaking slow devices.

-- 
bill davidsen <davidsen@....com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

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