On Wed, Nov 22, 2023 at 08:03:19PM +0000, Chun Ng wrote: > Hi, > > Recently I observed there is performance regression on system call mmap(..). I tried both vanilla kernels and Raspberry Pi kernels on a Raspberry Pi 4 box and the results are pretty consistent among them. > > Bisection showed that the regression starts from k-6.1, and the latest vanilla k-6.7 is still showing the same regression. > > The test program calls mmap/munmap for a 4K page with MAP_ANON and MAP_PRIVATE flags, and ftrace is used to measure the time spent on the do_mmap(..) call. Measured time of a sample run with different vanilla kernel versions are: > k-5.10 and k-6.0: ~157us > k-6.1: ~194us > k-6.7: ~214us > Results are pretty consistent across multiple runs with a small percentage variance. Ftrace shows that latency of mmap_region(...) has increased since k-6.1. An application that makes frequent mmap(..) calls the accumulated extra latency is very noticeable. Did you mean that v6.0 doesn't have this regression? Confused... -- An old man doll... just what I always wanted! - Clara
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