Re: Pistachio IPC performance on Bare Metal

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Hi Matt,

Am 20.09.2014 um 01:03 schrieb matthew scaperoth:
> My question really is how to optimize. I would like to get intra
> process IPC down to < 200 cycles, but I've sort of hit a wall. I do
> have fast path enabled and debugging disabled. The code I altered was
> pingpong and I simply removed the loops and message register
> iteration so that I could perform a single IPC. I wrapped the IPC
> call with two variables that catch the clock time before and after
> the IPC. I do this several thousand times and take an average.
>=20
> Any ideas on what I am doing wrong?

After skimming through your code, I believe the problem is that you try
to measure the latency of each individual IPC message. I didn't check
how exactly the functions you are using take the time, but it's very
possible that their resolution is not high enough to measure individual
IPC messages. In addition, there is overhead associated with calling
those functions. If you call them once per IPC message, that overhead
adds up, which might explain the long IPC latencies you're seeing. The
original pingpong instead takes the time for n IPC messages and divides
by n. That averages out both the inaccuracy of the clock itself and the
overhead associated with reading it.

HTH

Jens

--=20
Karlsruhe Institute of Technology (KIT)
Operating Systems Group

Dipl.-Inform. Jens Kehne
Researcher

Am Fasanengarten 5
Building 50.34
76131 Karlsruhe, Germany

Phone: +49 721 608-42645
Fax: +49 721 608-47664
Email: kehne@kit edu
Web: http://www.kit.edu/

KIT =96 University of the State of Baden-Wuerttemberg and
National Research Center of the Helmholtz Association


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