Re: RFC for a new Scheduling policy/class in the Linux-kernel

Peter Zijlstra
2009-07-13T17:28:30Z

On Mon, 2009-07-13 at 17:44 +0200, Raistlin wrote:
> What we would like to achieve is some set of rules that, extending the
> UP ones, yield a situation which is both:
> - analyzable from the real-time theorist's point of view... Which is
> (un?)fortunately what we are :-)
> - possible to implement... Which is not always (un!)fortunately obvious
> here :-)

I would very much like a proper theoretical foundation for whatever we
end up with ;-)

> Very basically: from the analysis point of view one easy and effective
> solution would be to have the blocked-running tasks --i.e., the tasks
> blocked on some lock that have been left on the rq to proxy-execute the
> lock owner-- busy waiting while the lock owner is running. This allows
> for retaining a lot of nice properties BWI already has, as far as
> analyzability is concerned.

Right, practically we cannot do this, since we expose the block graph to
userspace and you could in userspace construct a program that would
exploit this spinning to DoS the system.