On 05/03/2005 09:12 AM Der Herr Hofrat wrote: >> Hello, >> >> I just run flushy on a low-end PowerPC system: >> >> XPC855xxZPnnD4 at 80 MHz: 4 kB I-Cache 4 kB D-Cache FEC present >> >> Unfortunately the results are not that clear than expected. I see the >> latency going up a bit but other activities do increase it as well >> (telnet, ping -f). Furthermore, from run to run the latency results are > > did some measurements on a number of boxes and ping -f is a bad test as > especially on low end systems it results in the kernel more or less running > the same code in an infinite loop - resulting in "good" values. If you want > to see the network layer influence use NetPIPE and see the jitter jump ;) > >> different. Well, I think it's a complex and arch-dependent interplay of >> various parameters, e.g. on the system above, the caches are quite small >> and therefore the influence of cache refills is low. When I have more >> time I might repeat the tests on other PowerPC archs as well. >> >> >> Apart from that, you can do little to reduce the latency degradation due >> to cache refills and TLB misses (at least not in a portable way). Linux >> simply requires it. >> > has anybody ever used gcov feedbacks for ppc ? (run load with kernel compiled > with -fprofile-arcs recompile -fbranch-probabilities rerun load and test > jitter) . The PPC branch prediction should be almost ideal for this and that > would be a fairly portable way of doing it.
I never tried that but I doubt that it will reduce cache refills and TLB misses. I will have a closer look when time permits. Wolfgang.
