linux-kernel - Re: [PATCH 0/2] x86: Speed up ioremap operations

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Message-Id: <20140827160610.4ef142d28fd7f276efd38a51@linux-foundation.org>
Date:	Wed, 27 Aug 2014 16:06:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mike Travis <travis@....com>
Cc:	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
	msalter@...hat.com, dyoung@...hat.com, riel@...hat.com,
	peterz@...radead.org, mgorman@...e.de,
	linux-kernel@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/2] x86: Speed up ioremap operations

On Wed, 27 Aug 2014 17:59:27 -0500 Mike Travis <travis@....com> wrote:

> 
> We have a large university system in the UK that is experiencing
> very long delays modprobing the driver for a specific I/O device.
> The delay is from 8-10 minutes per device and there are 31 devices
> in the system.  This 4 to 5 hour delay in starting up those I/O
> devices is very much a burden on the customer.

That's nuts.

> There are two causes for requiring a restart/reload of the drivers.
> First is periodic preventive maintenance (PM) and the second is if
> any of the devices experience a fatal error.  Both of these trigger
> this excessively long delay in bringing the system back up to full
> capability.
> 
> The problem was tracked down to a very slow IOREMAP operation and
> the excessively long ioresource lookup to insure that the user is
> not attempting to ioremap RAM.  These patches provide a speed up
> to that function.

With what result?
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