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SubjectRe: [CFT][RFC] HT scheduler


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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