Re: [CFT][RFC] HT scheduler

[Nick Piggin]

Jamie Lokier wrote:

> Nick Piggin wrote:
>
> > > Shared runqueues sound like a simplification to describe execution units
> > > which have shared resourses and null cost of changing units. You can do
> > > that by having a domain which behaved like that, but a shared runqueue
> > > sounds better because it would eliminate the cost of even considering
> > > moving a process from one sibling to another.
> > You are correct, however it would be a miniscule cost advantage,
> > possibly outweighed by the shared lock, and overhead of more
> > changing of CPUs (I'm sure there would be some cost).
>
> Regarding the overhead of the shared runqueue lock:
>
> Is the "lock" prefix actually required for locking between x86
> siblings which share the same L1 cache?

That lock is still taken by other CPUs as well for eg. wakeups, balancing,
and so forth. I guess it could be a very specific optimisation for
spinlocks in general if there was only one HT core. Don't know if it
would be worthwhile though.


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