linux-kernel - Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11 (PCI_MULTITHREAD

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Date:	Wed, 9 May 2007 02:46:47 -0700
From:	Greg KH <greg@...ah.com>
To:	David Miller <davem@...emloft.net>
Cc:	torvalds@...ux-foundation.org, bunk@...sta.de,
	cornelia.huck@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11
	(PCI_MULTITHREAD_PROBE)

On Tue, May 08, 2007 at 02:15:54PM -0700, David Miller wrote:
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> Date: Tue, 8 May 2007 08:27:34 -0700 (PDT)
> 
> > Threading at the bus level just inevitably means things like random 
> > numbers for devices depending on some timing/scheduling issue. That's 
> > nasty.
> 
> I hadn't considered this issue, so ignore the other reply I made to
> this thread.  Although as an aside I'm starting to become of an
> opinion that device numbering doesn't matter.  Every device should
> have a unique ID of sorts, or a unique physical location, and that
> should factor into the thing users use to refer to the object.

We pretty much already do this today.

For block devices, as an example, look at /dev/disk/ which udev creates
so that you can handle block devices being discovered in any order
possible.

> Anyways, it would be nice, however, to really deal with the case like
> when the IDE layer is waiting for a probe to port X to timeout,
> meanwhile we could be initializing the networking card.
> 
> Another bad case is, as you mentioned, SCSI bus resets and SAS/FC
> fabric scans.  Those take several seconds if not longer and it's
> really stupid to not be able to do other things during that time.

Yes, because of that, I think this kind of multi-probe stuff should be
done in the IDE/SATA/SCSI bus code, not in the PCI code, as PCI
"normally" does not have any speed issues.

thanks,

greg k-h
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