Call for performance evaluation: net.isr.direct (fwd)
Andrew Gallatin
gallatin at cs.duke.edu
Thu Oct 13 16:55:03 PDT 2005
Garrett Wollman writes:
> <<On Wed, 12 Oct 2005 17:17:12 -0400 (EDT), Andrew Gallatin <gallatin at cs.duke.edu> said:
>
> > Right now, at least, it seems to work OK. I haven't tried witness,
> > but a non-debug kernel shows a big speedup from enabling it. Do
> > you think there is a chance that it could be made to work in FreeBSD?
>
> I did this ten years ago for a previous job and was able to blow out
> the stack very easily.
I haven't blown it out yet, but for that and other reasons, it seems
to be a bigger can of worms than it would be worth.
The interesting thing is that using the TSC timecounter rather than
ACPI-fast reduces the context switch latency enough so as to make the
TCP latency 25us when using a netisr thread. 25us is identical to
what I saw with the direct dispatch loopback hack.
Linux already takes care of syncing the TSC between SMP cpus, so we
know it is possible. This seems like a much more doable optimization.
And it is likely to have other benefits..
Drew
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