Influence of application priority on IPC

Udo Steinberg udo at ...121...
Mon Nov 12 14:28:16 CET 2012

On Mon, 12 Nov 2012 12:24:04 +0100 Alexander Boettcher (AB) wrote:

AB> On 12.11.2012 10:27, Norman Feske wrote:
AB> > processes the execution flows through. As far as I know, NOVA is the
AB> > only kernel of the Genode base platforms that properly implements
AB> > priority inheritance.
AB> Just some note for completeness: This is solely implemented for the IPC
AB> mechanism of the kernel, however it is not supported for the semaphores
AB> provided by the kernel. That means if semaphores are used as locks to
AB> protect some critical section in user mode, the thread running inside
AB> the critical section (and holding the lock) doesn't inherit the priority
AB> of other threads also attempting to get into the same critical section.

We don't do it for semaphores, because semaphores can be used from different
cores and cross-core inheritance doesn't work. We could add some limited
form of local inheritance to semaphores, e.g. threads on the same core could
help each other.

But - having only core-local inheritance for semaphores could lead to odd
behavior, such as programs working as expected on a single-core machine and
breaking when running on a multi-core machine, because a developer may have
built assumptions about priority inheritance into their code.

So... how useful would core-local inheritance for semaphores be?

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