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

From: Mike Travis
Date: Wed Aug 27 2014 - 19:15:47 EST

On 8/27/2014 4:06 PM, Andrew Morton wrote:
> On Wed, 27 Aug 2014 17:59:27 -0500 Mike Travis <travis@xxxxxxx> 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.

Exactly! The customer was (as expected) not terribly pleased... :)
>> 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.]

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