53c984d976
This was part of a performance improvement made by CL 232298 to reduce timer latency. On multiprocessor Plan 9 machines, it triggers memory faults often enough that the builder test suite never completes successfully. See issue #42303 for discussion. As shown by the benchmark result below, worst case latency on plan9_arm is very bad even with the wakep call in place - in the tickers-per-P=1 case, a 3ms timer is 270ms late. Skipping the wakep call and running the benchmark again shows some cases worse, some better. The performance cost doesn't seem excessive for this temporary workaround which makes the plan9_arm builders usable again. With wakep call: cpu% go test -bench Latency time goos: plan9 goarch: arm pkg: time BenchmarkParallelTimerLatency-4 100 10985859 avg-late-ns 18630963 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=1-4 195 270294688 avg-late-ns 542057670 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=2-4 234 182452000 avg-late-ns 423933688 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=3-4 280 193003004 avg-late-ns 408034405 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=4-4 282 132819086 avg-late-ns 313624570 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=5-4 339 71152187 avg-late-ns 189014519 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=6-4 315 26860484 avg-late-ns 101759844 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=7-4 357 19106739 avg-late-ns 59435620 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=8-4 376 7246933 avg-late-ns 38888461 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=9-4 267 40476892 avg-late-ns 205851926 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=10-4 294 87836303 avg-late-ns 252059695 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=2ms/tickers-per-P=1-4 379 4127144 avg-late-ns 10494927 max-late-ns Without wakep call: BenchmarkParallelTimerLatency-4 61 10775151 avg-late-ns 18668517 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=1-4 199 299587535 avg-late-ns 597182307 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=2-4 272 184561831 avg-late-ns 449739837 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=3-4 235 154983257 avg-late-ns 370940553 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=4-4 290 150034689 avg-late-ns 332399843 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=5-4 298 47540764 avg-late-ns 133709031 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=6-4 350 20379394 avg-late-ns 81742809 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=7-4 363 14403223 avg-late-ns 98901212 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=8-4 375 12293090 avg-late-ns 50266552 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=9-4 336 40628820 avg-late-ns 150946099 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=300µs/tickers-per-P=10-4 289 88265539 avg-late-ns 280770418 max-late-ns BenchmarkStaggeredTickerLatency/work-dur=2ms/tickers-per-P=1-4 375 8364937 avg-late-ns 22598421 max-late-ns Fixes #42303 Change-Id: I70c63cb2a2bad46950a7cd9dfc7bb32943710d32 Reviewed-on: https://go-review.googlesource.com/c/go/+/275672 Reviewed-by: David du Colombier <0intro@gmail.com> Trust: Michael Pratt <mpratt@google.com> |
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