linux-kernel - Re: block layer runtime pm and udisks

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Date:	Thu, 10 Oct 2013 09:52:57 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Phillip Susi <psusi@...ntu.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <axboe@...nel.dk>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Tejun Heo <tj@...nel.org>
CC:	linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	Aaron Lu <aaron.lwe@...il.com>,
	Shane Huang <shane.huang@....com>,
	Oliver Neukum <oneukum@...e.de>
Subject: Re: block layer runtime pm and udisks

On 10/10/2013 09:40 AM, Phillip Susi wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
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> I have been trying out the new block layer runtime pm, and run into a
> problem: udisks keeps waking up the disk.  Every 10 minutes it tries
> to poll the SMART status of the drive, but it does first issue an ata
> CHECK POWER command to see if it is in standby, and skips the check to
> avoid waking the disk.  The problem with runtime pm is that *any*
> request brings the drive out of suspend, and the suspend wake path
> forces the drive to spin up by issuing a verify command on sector 0.
> 
> Is there a reason that the wakeup path forces the drive to spin up, or
> could this be removed and rely on the drive waking up automatically if
> the request requires it?
> 
> Or would it be possible to notice that the command being sent is a
> check power command, and fake the reply instead of resuming the device?
> 
> Or does udisks just need to check the runtime pm status before trying
> the check power command?

I think the udisks can be modified to check if the drive is runtime
suspended and if so, avoid poll the SMART status.

Thanks,
Aaron

> 
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