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Alexander Kanavin
8282240ec1
TL;DR version: with this, and the previous compression level changes I am seeing drastic speedups in package_write_rpm completion times: webkitgtk goes from 78 seconds to 37 seconds glibc-locale goes from 399 seconds to 58 seconds (!) The long version: rpm uses multithreading for two purposes: - spawning compressors (which are nowadays themselves multi-threaded, so the feature is not as useful as it once was) - parallel file classification While the former behaves well on massively parallel CPUs (it was written and verified here :), the latter was then added by upstream and only benchmarked on their very old, slow laptop, apparently: https://github.com/rpm-software-management/rpm/commit/41f0e214f2266f02d6185ba11f797716de8125d4 On anything more capable it starts showing pathologic behavior, presumably from spawning massive amount of very short-lived threads, and then having to synchronize them. For example classifying glibc-locale takes 5m20s with 256 threads (default on my machine!) 1m49s with 64 threads 59s with 16 threads 48s with 8 threads Even a more typical recipe like webkitgtk is affected: 47s with 256 threads 32s with 64 threads 27s with 16 or 8 threads I have found that the optimal amount is actually four: this also means that only four compressors are running at a time, but as they're themselves using threads, and typical recipes are dominated by just two or three large packages, this does not affect overall completion time. (From OE-Core rev: ac480775440fba812fd5aa9da73e0e5bc60d46d6) Signed-off-by: Alexander Kanavin <alex@linutronix.de> Signed-off-by: Steve Sakoman <steve@sakoman.com>