Perfcounters added to the mainline
Posted Jul 2, 2009 3:39 UTC (Thu) by jreiser
Parent article: Perfcounters added to the mainline
Linux does not use coloring algorithms when allocating page frames to virtual addresses. On popular architectures with large caches and small pages and small associativity (including x86 of the last few years) most statistics on cache misses are subject to large variances because of the uneven mapping of virtual address space to physical cache lines. The statistics have only small predictive value, and thus are little help to application programmers. I have seen the numbers vary by 15% for consecutive invocations of the same long-running CPU-bound deterministic program on the same data (the sequence of virtual addresses accessed by each run was identical) on an "otherwise idle" machine. Do not use the output of perf stat to tune your application.
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