Re: [RFC v2 3/6] kthread: warn on kill signal if not OOM

[Dmitry Torokhov]

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:
> > On Tuesday, September 09, 2014 03:46:23 PM James Bottomley wrote:
> > > On Wed, 2014-09-10 at 07:41 +0900, Tejun Heo wrote:
> > > > 
> > > > 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
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