Re: Possible case of sched_ule never honoring cpu_set affinity?

On Tuesday 24 February 2009 5:46:11 pm Justin Teller wrote:
> I believe I've found a case where sched_ule can never honor cpu_set
> affinity, and I've attached a suggestion to fix it -- if I'm way off
> on how this should be implemented, please let me know!
> 
> Imagine the case where sched_affinity is called and the thread is on a
> RUNQ on the wrong CPU -- sched_affinity simply exits, relying on
> something else in the scheduler to migrate the thread if need be.  The
> next time the thread is chosen to run, it runs on the wrong CPU.
> Worse, if the thread never goes to sleep or is chosen to be moved by
> the load balancer, the thread will continue running on the wrong CPU
> indefinitely.
> 
> Attached is a suggestion of how to change the scheduler to honor
> affinity in this case.  With the attached diff, sched_ule will allow a
> thread to run on the wrong CPU for one slice.  Then when the thread
> moves through sched_switch, if it was running on the wrong CPU, it
> will be migrated to the right CPU.  I've written a test where one
> thread will bind another thread to a particular CPU (using cpusets)
> then waits until it's running on the right CPU before binding it to a
> different CPU (and continuing ad nauseam).  Without the change, the
> test will sometimes hang waiting for the second thread to get on the
> correct CPU -- with the change, it works every time.

I think your patch is correct.

-- 
John Baldwin