Re: [PATCH 2/3] mm, x86: Remove region_is_ram() call from ioremap

Ingo Molnar
2015-06-23T09:02:48Z

* Mike Travis <travis@sgi.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