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Date:	Thu, 11 Sep 2014 13:23:54 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Tejun Heo <tj@...nel.org>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay@...y.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Wu Zhangjin <falcon@...zu.com>, Takashi Iwai <tiwai@...e.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>, hare@...e.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Benjamin Poirier <bpoirier@...e.de>,
	Santosh Rastapur <santosh@...lsio.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tim Gardner <tim.gardner@...onical.com>,
	Pierre Fersing <pierre-fersing@...rref.org>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Cas ey Leedom <leedom@...lsio.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	MPT-FusionLinux.pdl@...gotech.com,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC v2 3/6] kthread: warn on kill signal if not OOM

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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