Re: set_cpus_allowed() optimization

[Robert Love]

n Fri, 2002-05-10 at 13:09, Mike Kravetz wrote: 
> Please consider the following optimization to set_cpus_allowed().
> In the case where the task does not reside on a runqueue, is it
> not safe/sufficient to simply set the task's cpu field?  This
> would avoid scheduling the migration thread to perform the task.
> 
> Previously, set_cpus_allowed() was always called for a task that
> resides on a runqueue.  With the introduction of the 'cpu affinity'
> system calls, this is no longer the case.

I like!  I agree, if the task is not runnable then it should be
sufficient to just set task->cpu as when it is activated it will be put
into the runqueue based on ->cpu.

There was a chance even without the CPU affinity runqueues a process
would dequeue before set_cpus_allowed returned.  Look at the case in
migration_thread where exactly what your patch does is done.  If !array,
then the code just sets task->cpu and returns.

Ingo?  Good?

	Robert Love