Re: MSI interrupts

In article <jwvjz8coho7.fsf-monnier+comp.arch@gnu.org>,
Stefan Monnier  <monnier@iro.umontreal.ca> wrote:

Dan Cross [2025-03-25 22:19:07] wrote:

From what I gather, you've said to just eschew the atomic event
stuff and build a traditional lock using those primitives.  But
you have also said that a traditional lock can be silently
unlocked if the thread holding it (which, apparently, is an
abstraction known to hardware) is preempted.  It will be like
the lock had never been acquired.

>
Here's the misunderstanding: the lock that can be silently taken away
is the lock implemented in the CPU to run an ATOMIC sequence, not the
lock implemented as a data-structure on top of it: once you've run
(atomically) your `lock_acquire`, of course that lock is yours.  The CPU
doesn't even know that this data-structure is a lock and has no
way to steal it.

I hope you are right, and I'd like Mitch to confirm.

Even so, I don't see the point of the proposed atomic framework.
It seems to have no significant advantage over a more
traditional scheme; CAS, LL-SC, whatever seem more general and
less intertwined with primitives that the hardware has no real
business injecting itself into (like threads).

- Dan C.