Re: [PATCH 1/3] sd: don't bother spinning up disks on resume

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On 11/17/2013 8:06 PM, Phillip Susi wrote:
> I don't see anything particularly inefficient about issuing the
> command in the eh path ( in fact, libata always uses the eh path to
> handle power management ).  You can of course, use the
> manage_start_stop flag to have the disk start on resume if you
> really want.

Yikes, I think I see now why scsi eh is so bad: the entire host, not
just the device is quiesced.

I suppose now the question is how to issue the START STOP UNIT from
sd_prep_fn()?  I gather you can't just call scsi_execute_req() from
there?  Is there maybe a way to insert a START STOP UNIT request into
the queue ahead of the current request being prepped?  Can
sd_prep_fn() be called concurrently on multiple cpus?  Hrm.. what
about TCQ?  Would it be bad if the original request were queued ( to
the drive ) before the START STOP UNIT command completed?

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