On Thu, Sep 11, 2014 at 12:59:25PM -0700, James Bottomley wrote:

On Tue, 2014-09-09 at 16:01 -0700, Dmitry Torokhov wrote:

quoted

On Tuesday, September 09, 2014 03:46:23 PM James Bottomley wrote:

quoted

On Wed, 2014-09-10 at 07:41 +0900, Tejun Heo wrote:

quoted

The thing is that we have to have dynamic mechanism to listen for
device attachments no matter what and such mechanism has been in place
for a long time at this point.  The synchronous wait simply doesn't
serve any purpose anymore and kinda gets in the way in that it makes
it a possibly extremely slow process to tell whether loading of a
module succeeded or not because the wait for the initial round of
probe is piggybacked.

OK, so we just fire and forget in userland ... why bother inventing an
elaborate new infrastructure in the kernel to do exactly what

modprobe <mod> &

would do?

Just so we do not forget: we also want the no-modules case to also be able
to probe asynchronously so that a slow device does not stall kernel booting.

Yes, but we mostly do this anyway.  SCSI for instance does asynchronous
scanning of attached devices (once the cards are probed)

What would it do it card was a bit slow to probe?

but has a sync
point for ordering.

Quite often we do not really care about ordering of devices. I mean,
does it matter if your mouse is discovered before your keyboard or
after?

The problem of speeding up boot is different from the one of init
processes killing modprobes.

Right. One is systemd doing stupid things, another is kernel could be
smarter.

 There are elements in common, but by and
large the biggest headaches at least in large device number boots have
already been tackled by the enterprise crowd (they don't like their
S390's or 1024 core NUMA systems taking half an hour to come up).

Please do not position this as a mostly solved large systems problem,
For us it is touchpad detection stalling kernel for 0.5-1 sec. Which is
a lot given that we boot in seconds.

Thanks.

-- 
Dmitry