https://bugs.kde.org/show_bug.cgi?id=380942
--- Comment #1 from Julian Seward <jsew...@acm.org> --- Created attachment 105965 --> https://bugs.kde.org/attachment.cgi?id=105965&action=edit Initial implementation Here's an initial implementation. Some notes: * You *must* use --fair-sched=yes. If you don't, you'll get garbage results and no warning. * The implementation reduces SCHEDULING_QUANTUM from 100000 to 1200, so as to give reasonable pseudo-parallel interleaving of threads. That is a fine enough interleaving to pick up more than 90% of all RFOs from execution of parallel layout algorithms in Firefox. If you have very frequent cache line transfers then you may need to set this even lower to get accurate stats. * The reduction in SCHEDULING_QUANTUM makes Valgrind run more slowly, although not catastrophically so. * This doesn't really simulate the MESI protocol directly. Instead it keeps track of which thread has most recently accessed each cache line sized piece of memory, and observes transfers of ownership between these cache line sized pieces of memory. * As a result you can simulate MESI (like) behaviour for any number of threads. It's unrelated to the hardware in your machine. The line size is currently hardwired to 64 bytes. * Use the flag --simulate-mesi=yes. You can't use any of the other Callgrind simulation facilities (caches, branches, prefetchers etc) at the same time. * The simulation tries to distinguish between true and false sharing. * This is all very experimental. It's not really clear whether the RFO detection and the true-vs-false sharing detection reflect reality accurately enough to be useful. * 4 different kinds of costs are computed: RFOr -- requests for ownership (transfers) due to reads RFOw -- RFOs due to writes RFOrTrue -- RFOs due to reads, with true sharing RFOwTrue -- RFOs due to writes, with true sharing * You can display the results in KCachegrind in the normal way. * Although it is not necessary, it is useful to program the following formulas into KCachegrind: RFO = RFOr + RFOw -- total number of RFOs RFOTrue = RFOrTrue + RFOwTrue -- total number of RFOs from true sharing RFOFalse = RFOr + RFOw - RFOrTrue - RFOwTrue -- total number of RFOs from false sharing -- You are receiving this mail because: You are watching all bug changes.
