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

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Message-Id: <20140827162006.580e83d57696b5eba203b18c@linux-foundation.org>
Date:	Wed, 27 Aug 2014 16:20:06 -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 16:15:28 -0700 Mike Travis <travis@....com> wrote:

> 
> > 
> >> 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?
> > 
> 
> Early measurements on our in house lab system (with far fewer cpus
> and memory) shows about a 60-75% increase.  They have a 31 devices,
> 3000+ cpus, 10+Tb of memory.  We have 20 devices, 480 cpus, ~2Tb of
> memory.  I expect their ioresource list to be about 5-10 times longer.
> [But their system is in production so we have to wait for the next
> scheduled PM interval before a live test can be done.]

So you expect 1+ hours?  That's still nuts.
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