Changing Affinity of Executing Thread
sebastian.huber at embedded-brains.de
Tue May 20 06:18:25 UTC 2014
On 2014-05-20 01:39, Joel Sherrill wrote:
> I have set affinity and unblock logic in place and am testing scenarios.
> I still have to work on blocking.
> I am playing with a scenario now that changes the affinity of a thread
> that is executing. I am concerned that changing the affinity of a thread
> that is executing may have a window to address similar to restart of
> self. You are still executing on the core but could be moved as part of
> setting affinity.
> Before the set affinity of smp1 to core 1 is executed, the set of the
> EXECUTING / HEIR / SWITCH NEEDED
> CPU 0: 0x0a010004 @ 5 / 0x0a010004 @ 5 false (smp4)
> CPU 1: 0x0a010003 @ 6 / 0x0a010003 @ 6 false (smp3)
> CPU 2: 0x0a010002 @ 6 / 0x0a010002 @ 6 false (smp2)
> CPU 3: 0x0a010001 @ 5 / 0x0a010001 @ 5 false (smp1)
> When set affinity internally sets the state of smp1 to STATES_MIGRATE,
> the heir on cpu 3 is changed to smp5.
> The affinity is updated and when STATES_MIGRATE is cleared, smp1 is
> declared heir on cpu 2.
> It is still executing on cpu 3 when it is declared heir on cpu 2.
> Wouldn't changing the scheduler for the executing thread have
> a similar issue? You need to finish up the thread with one scheduler
> before moving it.
This is not a problem since this commit:
The key point is that the is executing indicator moved to the thread context
and the low-level context switch is responsible for it. There exists a point
in time on which a processor executes no context during a context switch.
> What happens if you end up with a combination of these
> actions at the same time? restart, scheduler change, affinity change.
Currently a scheduler change must not be issued in interrupt context. Apart
from this everything works fine even if you restart a thread during a scheduler
change since thread dispatching is disabled.
Sebastian Huber, embedded brains GmbH
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