Hi, Another thing to watch out is user vs. kernel. I have changed the logic inside libpfm4. If you're using the latest version it measures user+kernel execution. The kernel may touch the memory before you do. Thus, changing the optimization level may not impact your results.
You can try forcing user level only: ./task -e LLC_MISSES:u,LLC_REFERENCES:u ./mcol And yes, make sure the compiler is not playing games on you. On Tue, Sep 14, 2010 at 12:07 AM, Vince Weaver <vweav...@eecs.utk.edu> wrote: > On Mon, 13 Sep 2010, DRAM Ninjas wrote: >> Thanks for your reply. I've tried with -O0 and without any optimization >> flags (not sure what gcc >> defaults to, now that I think about it) and I get roughly the same thing. If >> I print out the values of >> the two sums, that will force it to not optimize them out, right? > > yes. You have to be careful when you use no optimizations, because the > compiler generates really naive code in that case. Have you checked the > assembly output generated by the compiler yet? > >> And your point about being impossible to correlate measured to expected, >> could you provide any more >> insight? I'm quite baffled at the miss rates for workloads that I know will >> miss _every_ access in the >> main program loop (i.e. random memory walks in large array). > > You can look at the presentations here: > http://www.cs.utk.edu/~vweaver1/presentations/ > > These are recent results (so no paper-length versions of them yet). You > want the slides at the end that show cache miss results for various x86_64 > processors. This is for a very simple array-walk workload, and the > results are very hard to interpret. In no case were the results ever the > "expected" result, even when doing backward or random strides. > > My entire PhD thesis was on my attempt to match perf-counters to simulator > results. It turns out to be very difficult on anything more recent > than a MIPS R12000. > > Vince > ------------------------------------------------------------------------------ > Start uncovering the many advantages of virtual appliances > and start using them to simplify application deployment and > accelerate your shift to cloud computing. > http://p.sf.net/sfu/novell-sfdev2dev > _______________________________________________ > perfmon2-devel mailing list > perfmon2-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/perfmon2-devel > > ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
