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On Wednesday 16 July 2008 08:26, Mathieu Desnoyers wrote: > Instrumentation of waits caused by memory accesses on mmap regions. > > Those tracepoints are used by LTTng. > > About the performance impact of tracepoints (which is comparable to > markers), even without immediate values optimizations, tests done by Hideo > Aoki on ia64 show no regression. His test case was using hackbench on a > kernel where scheduler instrumentation (about 5 events in code scheduler > code) was added. See the "Tracepoints" patch header for performance result > detail. BTW. this sort of test is practically useless to measure overhead. If a modern CPU is executing out of primed insn/data and branch prediction cache, then yes this sort of thing is pretty well free. I see *real* workloads that have got continually and incrementally slower eg from 2.6.5 to 2.6.20+ as "features" get added. Surprisingly, none of them ever showed up individually on a microbenchmark. OK, for this case if you can configure it out, I guess that's fine. But let's not pretend that adding code and branches and function calls are ever free. | ||||||||||
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