Re: [PATCH 1/2] sched/wait: Break up long wake list walk

[Andi Kleen]

> > Still, generating such a migration storm would be fairly tricky I think.
> 
> Well, Mel seems to have been unable to generate a load that reproduces
> the long page waitqueues. And I don't think we've had any other
> reports of this either.

It could be that it requires a fairly large system. On large systems
under load a lot of things take much longer, so what's a tiny window on Mel's
system may suddenly be very large, and with much more threads 
they have a higher chance of bad interactions anyways.

We only see it on 4S+ today. But systems are always getting larger,
so what's a large system today, will be a normal medium scale system
tomorrow.

BTW we also collected PT traces for the long hang cases, but it was
hard to find a consistent pattern in them.

-Andi