Re: [ECOS] pthread processor binding

[Andrew Lunn <andrew at lunn dot ch>]

On Wed, Feb 14, 2007 at 04:07:56PM -0800, Ahmed Abdelkhalek wrote:
> Hi everyone,
> 
> Some pthread implementations allow binding a thread
> for execution on a particular processor or a set of
> processors (google pthread_pset_bind_np). Are there
> plans to include this in future ecos realeases?

Just thinking aloud here...

With an ROTS, which implements prioritized threads, the scheduler runs
the highest priority runnable thread. With SMP, it runs the highest
priority runnable threads, which could potentially be at different
priorities, but i don't think that really matters. You probably get
better performance if you have some level of processor affinity,
i.e. if possible run a thread on the same CPU as it was run last time,
with the hope it still has something useful in the cache. However a
runnable thread should not be left runnable but not run because the
last CPU it ran on is busy when another CPU is available. If you did
leave the thread runnable, you have to either leave the CPU unused,
which is probably wasteful or run a thread of lower priority. That
goes against the principle of the highest priority runnable threads
are the once that runs.

So to me, it seems like in an SMP RTOS, binding threads to processors
to will actually hinder RT operation.

   Andrew

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