2 ms·

No VM, no container. I could check the asm later on but sqrtrec is likely "free" because it was optimized away, no fences in the code neither so this might be a

• ori_b 1y ago
  Are you sure they're outliers? Here's someone else with similar results: https://arkanis.de/weblog/2017-01-05-measurements-of-system-call-performance-and-overhead/ https://arkanis.de/weblog/2017-01-05-measurements-of-system-... Google also reported similar numbers in 2011, when publicizing their fiber work. I can also get similar numbers (~68ns) on 9front, though a little higher.
  • menaerus 1y ago
    Data suggests that they are, and common sense too. And your point of reference is a little bit problematic since there's no code attached so it's hard for people to validate the measurements. Since you have been laser-focused on sqrt "bad" performance, and obvious optimization with sqrtrec, but also decided to ignore the rest of the results, maybe you can explain why there is such a large difference in your measurements between seemingly very similar platforms in terms of compute. After all this is pure compute problem. For example, why does 4.9GHz CPU (AMD Ryzen™ 5 7545U) yield 2x to 4x worse results than 5.5GHz CPU (AMD Ryzen™ 7 9700X)? AMD Ryzen 7 9700X Desktop: ---------------------------------------------------------------------------- Benchmark Time CPU Iterations ---------------------------------------------------------------------------- bench_getuid 38.6 ns 38.5 ns 18160546 bench_getpid 39.9 ns 39.9 ns 17703749 bench_close 45.2 ns 45.1 ns 15711379 bench_syscall 42.2 ns 42.1 ns 16638675 bench_sched_yield 81.7 ns 81.6 ns 8623522 AMD Ryzen 5 PRO 7545U Laptop: ---------------------------------------------------------------------------- Benchmark Time CPU Iterations ---------------------------------------------------------------------------- bench_getuid 106 ns 106 ns 6581746 bench_getpid 111 ns 111 ns 6271878 bench_close 116 ns 116 ns 5944154 bench_syscall 85.9 ns 85.9 ns 7317584 bench_sched_yield 315 ns 315 ns 2249333
    • ori_b 1y ago
      Because the low power laptop part has rather different characteristics to the desktop part, according to CPUmark benchmarks. It's not surprising that the low power part is slower; it's surprising when the newer/faster part is significantly slower for pure CPU operations. Different compliation flags, I guess. Edit: And, apparently, because regardless of what I do with `cpupower`, and twiddling the governors, cpu frequency on this machine is getting scaled. I've run out of time to debug that, I'll update later. https://www.cpubenchmark.net/compare/6205vs6367vs4835/AMD-Ryzen-7-9700X-vs-AMD-Ryzen-5-PRO-7545U-vs-Intel-i5-12600H https://www.cpubenchmark.net/compare/6205vs6367vs4835/AMD-Ry... I'm not sure what's up with sched_yield. I can also replicate these numbers with `perf bench syscall basic`.
      • menaerus 1y ago
        I mean, the base and turbo frequency are about the same on both parts, and the workload is very very simple. Case where TDP would matter is with the workload sucking up all the power budget of a whole chip in which case frequency would have to be downscaled in order to remain within the limits. I doubt this is the case here but I guess this can also be measured if one is curious enough. In my case, only sqrt was slower, the rest was 2x faster on a more modern CPU. I reran the experiment in a VM, on a company's Xeon server clocked @2.2GHz, and results are again pretty much the same as before: ---------------------------------------------------------------------------- Benchmark Time CPU Iterations ---------------------------------------------------------------------------- bench_getuid 778 ns 778 ns 901999 bench_getpid 774 ns 774 ns 902699 bench_close 779 ns 779 ns 896939 bench_syscall 761 ns 761 ns 916941 bench_sched_yield 1121 ns 1121 ns 566012 bench_clock_gettime 22.1 ns 22.1 ns 31579512 bench_clock_gettime_tai 22.0 ns 22.0 ns 31502402 bench_clock_gettime_monotonic 22.1 ns 22.1 ns 31848177 bench_clock_gettime_monotonic_raw 22.4 ns 22.4 ns 30953415 bench_nanosleep0 57424 ns 6967 ns 98218 bench_nanosleep0_slack1 6342 ns 6340 ns 110862 bench_nanosleep1_slack1 6310 ns 6308 ns 111064 bench_pthread_cond_signal 3.23 ns 3.23 ns 216726274 bench_assign 0.323 ns 0.323 ns 1000000000 bench_sqrt 2.64 ns 2.64 ns 265275643 bench_sqrtrec 4.40 ns 4.40 ns 160328959 bench_nothing 0.000 ns 0.000 ns 1000000000