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

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Message-ID: <20070508223653.1bb63b08@gondolin.boeblingen.de.ibm.com>
Date:	Tue, 8 May 2007 22:36:53 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Adrian Bunk <bunk@...sta.de>, Greg K-H <greg@...ah.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11
 (PCI_MULTITHREAD_PROBE)

On Tue, 8 May 2007 12:31:22 -0700 (PDT),
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > What if two devices become hotplugged at the same time? Does this imply 
> > that the bus _always_ needs to do some serializing there?
> 
> You want to test it? Be my guest.

It was more a rhetorical question. If not all drivers can handle it,
serialize at the bus level. But if all drivers can, there's no reason
for the bus to do it. On a bus with a small number of drivers, I
prefer to have the drivers in good shape. (This kind of implies that e.
g. pci needs to serialize, but css/ccw doesn't, and doesn't have to.)

> But the final nail in the coffin is that doing it at the bus level is 
> INFERIOR. As you yourself admitted, it's better to do some things 
> synchronously.

How so? It is possible to do some stuff synchronously. But why
shouldn't other things be done asynchronously?
(And there is a place both for bus-level parallelism and driver-level
parallelism. Just depends on your bus/driver/device.)
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