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Date: Wed, 27 Aug 2014 16:20:06 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Mike Travis <travis@sgi.com>
Cc: mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, msalter@redhat.com,
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        mgorman@suse.de, linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 0/2] x86: Speed up ioremap operations
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On Wed, 27 Aug 2014 16:15:28 -0700 Mike Travis <travis@sgi.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.