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Re: USB storage no-boot regression (bisected)

From:  Alan Cox <alan-qBU/x9rampVanCEyBjwyrvXRex20P6io-AT-public.gmane.org>
To:  Mark Lord <lkml-gsilrlXbHYg-AT-public.gmane.org>
Subject:  Re: USB storage no-boot regression (bisected)
Date:  Wed, 15 Apr 2009 16:01:53 +0100
Message-ID:  <20090415160153.485c2095@lxorguk.ukuu.org.uk>
Cc:  Greg KH <greg-U8xfFu+wG4EAvxtiuMwx3w-AT-public.gmane.org>, Jeff Garzik <jeff-o2qLIJkoznsdnm+yROfE0A-AT-public.gmane.org>, Linux USB kernel mailing list <linux-usb-u79uwXL29TY76Z2rM5mHXA-AT-public.gmane.org>, Alan Stern <stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz-AT-public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA-AT-public.gmane.org>, "Rafael J. Wysocki" <rjw-KKrjLPT3xs0-AT-public.gmane.org>, Arjan van de Ven <arjan-wEGCiKHe2LqWVfeAwA7xHQ-AT-public.gmane.org>
Archive-link:  Article, Thread

> SATA drives also take variable amounts of time to "show up" at boot.
> Perhaps Jeff should customize libata for your and Arjan's exact setups,
> just to help with understanding the point here.  :)

Actually I would argue the reverse. The sooner we can push this so that
libata isn't blocking mounting the rootfs the better.

> The speed ups are fine (and welcome), but we really now need
> Arjan to follow-up with a patch to have the kernel *by default*
> wait a little longer for the rootfs to show up.
> 
> Not forever, just a few seconds to compensate for the regression.

Why should every user suffer a slower boot and a poorer resume time ?

Instead make the root fs mounting look like this


	while(my_rootfs_hasnt_appeared_and_i_am_sad()) {
		wait_on(&new_disk_discovery);
	}

and poke the queue whenever we add a relevant device.

That way if you are booting off an initrd you can finish the SATA probe
in parallel to getting userspace ticking over.

On what is nowdays essentially a hot plug system it all needs turning
this way up - eg RAID volumes should assemble and come online as the
drives are discovered not at some fixed point later in userspace.

Alan
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