linux-kernel - Re: USB storage no-boot regression (bisected)

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Message-ID: <20090415160153.485c2095@lxorguk.ukuu.org.uk>
Date:	Wed, 15 Apr 2009 16:01:53 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Mark Lord <lkml@....ca>
Cc:	Greg KH <greg@...ah.com>, Jeff Garzik <jeff@...zik.org>,
	Linux USB kernel mailing list <linux-usb@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: USB storage no-boot regression (bisected)

> 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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