Re: [CFT][RFC] HT scheduler

[Nick Piggin]

Rusty Russell wrote:

> In message <3FE28529.1010003@xxxxxxxxxxxxxxx> you write:
>
> > + * See comment for set_cpus_allowed. calling rules are different:
> > + * the task's runqueue lock must be held, and __set_cpus_allowed
> > + * will return with the runqueue unlocked.
>
> Please, never *ever* do this.
>
> Locking is probably the hardest thing to get right, and code like this
> makes it harder.

Although in this case it is only one lock, and its only used in
one place, with comments. But yeah its far more complex than a
blocking semaphore would be.

> Fortunately, there is a simple solution coming with the hotplug CPU
> code: we need to hold the cpucontrol semaphore here anyway, against
> cpus vanishing.
>
> Perhaps we should just use that in both places.

We could just use a private semaphore until the hotplug code is in place.


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