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Re: DP performance

From: Marko Zec <zec@xxxxxxxx>
Date: Wed, 30 Nov 2005 19:03:56 +0100

On Wednesday 30 November 2005 03:08, Hiten Pandya wrote:
> Marko Zec wrote:
> > Should we be really that pessimistic about potential MP
> > performance, even with two NICs only?  Typically packet flows are
> > bi-directional, and if we could have one CPU/core taking care of
> > one direction, then there should be at least some room for
> > parallelism, especially once the parallelized routing tables see
> > the light.  Of course provided that each NIC is handled by a
> > separate core, and that IPC doesn't become the actual bottleneck.
> On a similar note, it is important that we add the *hardware* support
> for binding a set of CPUs to particular interrupt lines.

Yes that would be nice.  Alternatively one could have separate polling 
threads on per-CPU/core basis for handling different interfaces.  Maybe 
such a framework could even allow for migration of interfaces between 
polling threads, in order to dynamically adapt to different workloads / 
traffic patterns.  With hardware interrupts such an idea would be very 
difficult if not completely impossible to implement.


> I believe 
> that the API support for CPU-affinitized interrupt threads is already
> there so only the hard work is left of converting the APIC code from
> physical to logical access mode.
> I am not sure how the AMD64 platform handles CPU affinity, by that I
> mean if the same infrastructure put in place for i386 would work or
> not with a few modifications here and there.  The recent untangling
> of the interrupt code should make it simpler for others to dig into
> adding interrupt affinity support.

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