On Tue, 2015-06-23 at 11:01 +0200, Ingo Molnar wrote: > * Mike Travis <[email protected]> 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?
I agree that 15-20 minutes is till slow, but this slowness did not come from this ioremap RAM check because region_is_ram() used in this test had bugs, which led it return immediately. The slowness came from other places, such as page table initialization. I do not think the number of the resource table entries increase significantly on large systems. So, walk_system_ram_range() and fixed region_is_ram() should still perform fine on large systems. Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
