Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11 (PCI_MULTITHREAD_PROBE)

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 8 May 2007 12:31:22 -0700 (PDT),
Linus Torvalds <torvalds@linux-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.)