Re: workqueue thing

[Arjan van de Ven]

On 12/21/2009 15:19, Tejun Heo wrote:
> Ah... okay, there are two aspects cmwq invovles the scheduler.
>
> A. Concurrency management.  This is achieved by the scheduler
>     callbacks which watches how many workers are working.
>
> B. Deadlock avoidance.  This requires migrating rescuers to CPUs under
>     allocation distress.  The problem here is that
>     set_cpus_allowed_ptr() doesn't allow migrating tasks to CPUs which
>     are online but !active (CPU_DOWN_PREPARE).

why would you get involved in what-runs-where at all? Wouldn't the scheduler
load balancer be a useful thing ? ;-)


> For A, it's far more efficient and robust with scheduler callbacks.
> It's conceptually pretty simple too.

Assuming you don't get tasks that do lots of cpu intense work and that need
to get preempted etc...like raid5/6 sync but also the btrfs checksumming etc etc.
That to me is the weak spot of the scheduler callback thing. We already have
a whole thing that knows how to load balance and preempt tasks... it's called "scheduler".
Let the scheduler do its job and just give it insight in the work (by having a runnable thread)
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