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RE: [Xen-devel] ac_timer: time to say goodbye?

> What's heavyweight about it? We can maybe slim down the interface a 
> little, but we need a mechanism for managing at least an 
> alarm timeout 
> per vcpu. I don't imagine anyhting much simpler than ac_timer would 
> really fit the bill.
>   -- Keir
> Heavy weight? It's a basic heap (priority queue) implementation. 
> Seems to me like a perfectly sensible thing to have in a 
> hypervisor, and
> its used extensively by all the schedulers.
> Thanks,
> Ian

I can't say I fully understand the code and usage, so I may
be missing something, but...

Is there ever any more than one or two elements in the queue?
What is the total set of functions called by the queue?

> its used extensively by all the schedulers.

Try 'grep -r ac_timer' and see.

I suspect that the whole functionality of it can be replaced
with a couple of time variables that are checked and
manipulated in the timer interrupt code and a single
scheduler/timer routine in the generic scheduler.

The queueing mechanism is nice if there are a lot of uses,
but confusing (and IMHO heavyweight) if not.  I suspect
the generalized mechanism was good when there was more
functionality in Xen itself but as more and more migrates
to domain0, if the remaining usage could be replaced by
a couple variables, perhaps it should.

Not urgent, but if this is the right direction, we shouldn't
be layering more code on top of it (thus the suggestion of
deprecating it).


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