linux-kernel - Re: [PATCH 3/6] lguest suppress IDE probing

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Message-ID: <20070607144508.GV11115@waste.org>
Date:	Thu, 7 Jun 2007 09:45:08 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	bzolnier@...il.com, Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH 3/6] lguest suppress IDE probing

On Thu, Jun 07, 2007 at 12:13:07PM +1000, Rusty Russell wrote:
> On Wed, 2007-06-06 at 11:23 +0100, Alan Cox wrote:
> > > > Better yet just don't compile in the old IDE stuff, lguest doesn't have a
> > > > PCI or ISA bus anyway.
> > > 
> > > Sure, but the "run the same kernel as guest and host" is a really nice
> > > feature.
> > 
> > Modules dear boy, modules ;)
> 
> For some reason, pulling half the kernel's brains out into a separately
> maintained userspace seems to make things less reliable.  I always build
> in everything I need to boot.
> 
> Perhaps this makes me an old-timer.
> 
> > > > Alternatively make the IDE I/O space return 0xFF and it'll skip them
> > > > anyway.
> > > 
> > > Hmm, every "in" should be returning 0xFFs, but I still get the delay and
> > > the probing.  Xen domU gets it too.
> > 
> > Can you see in a debugger where it is spending the time. 0xFF should be
> > taken as "no port, move on nothing to see"
> 
> Well, the code is a little opaque to me, but do_probe() calls msleep(50)
> three times.  According to gdb this gets called 27 times -> 4.05
> seconds.

Yep. libata somehow manages to avoid most of these, it'd be
interesting to work out why.

-- 
Mathematics is the supreme nostalgia of our time.
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