Re: RPC overhead

[Ben Leslie]

On Mon Jul 07, 2008 at 17:00:58 +0200, Neal H. Walfield wrote:
>I ran an application benchmark on Viengoos.  Specifically, the
>application is derived from the GCbench program.  You can find it
>here:

>Each invocation includes approximately 12 words of payload and each
>reply contains 2 words.  This suggests an RPC overhead of 1350 cycles
>or 1.2 us.
>
>The 4.2 us represents approximately 5000 cycles.  This leaves 3650
>unaccounted cycles.  This seems to be a bit more than one can simply
>accounted to secondary cache effects, however, perhaps ping pong
>really measures the very hot case and I'm running with very cold
>caches.  I hope someone else can suggest how to figure out to what end
>these cycles are being put, has a theory, or can confirm that these
>cycle counts are not, in fact, too high.

That seem about right to me in terms of cache effects. ping-pong runs
very hot. Next step would be to turn on performance monitoring counters
and get a count of cache misses etc.

Cheers,

Benno