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

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Message-Id: <20140827225927.364537333@asylum.americas.sgi.com>
Date:	Wed, 27 Aug 2014 17:59:27 -0500
From:	Mike Travis <travis@....com>
To:	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com
Cc:	akpm@...ux-foundation.org, 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: [PATCH 0/2] x86: Speed up ioremap operations

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.

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.

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