Re: Poor performance of pthreads across cpu dies.
Re: Poor performance of pthreads across cpu dies.
- Subject: Re: Poor performance of pthreads across cpu dies.
- From: Andrew Gallatin <email@hidden>
- Date: Wed, 5 Sep 2007 16:46:04 -0400 (EDT)
Terry Lambert writes:
> On Sep 5, 2007, at 1:21 PM, Andrew Gallatin wrote:
> > Terry Lambert writes:
> >> From my reading of things, the issue as to whether or not you can
> >> target multiple CPUs with MSI has more to do with contiguous vs. non-
> >> contiguous vector assignment (which means that it's not possible in
> >> older Linux kernels). The MSI-X implementation overcomes this in
> >> older Linux kernels due to independent configuration of message data
> >> and address. BUT, if you are willing to perform contiguous
> >> allocations, it's not a problem for MSI to do the same.
> >
> > I'm not sure what linux kernels have to do with it.
>
> The limitation is an old Linux one, according to Intel.
>
> If you were to allocate 4 contiguous vectors, each vector could target
> a different ID, and the set of vectors could be associated with a
> single device.
>
> > The problem with
> > multiple messages in MSI is that all messages have the same message
> > address, but just different message data. Using the same message
> > address means that all interrupts will be delivered to the same
> > APIC, and hence to the same CPU. However, maybe this isn't a problem
> > on darwin/OSX, since all hardware interrupts are delivered to CPU 0
> > anyway...
>
> I think you missed where Mike pointed out that delivery is not as
> straight-forward as I initially said (I was mistaken, and Mike was
> correct here).
That is what I meant by "maybe this isn't a problem on darwin/OSX" :)
However, it is a problem in that our NIC uses MSI-X, and not multiple
MSI messages.
Drew
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