linux-kernel - Re: [PATCH 2/3] mm, x86: Remove region_is

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Date:	Tue, 23 Jun 2015 11:01:55 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Travis <travis@....com>
Cc:	Toshi Kani <toshi.kani@...com>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, akpm@...ux-foundation.org,
	roland@...estorage.com, dan.j.williams@...el.com, x86@...nel.org,
	linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
	Clive Harding <clive@....com>, Russ Anderson <rja@....com>
Subject: Re: [PATCH 2/3] mm, x86: Remove region_is_ram() call from ioremap


* 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.
> ...
> 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.
> >>>
> 
> The speed up was pretty dramatic, I think to about 15-20 minutes
> (the test was done by our local CS person in the UK).  I think this
> would prove the function was working since it would have fallen
> back to the previous page_is_ram function and the 4 to 5 hour
> startup.

Btw., I think even 15-20 minutes is still in the 'ridiculously slow' category.
Any chance to fix all of this properly, not just hack by hack?

Thanks,

	Ingo
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