> 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. hofrat
