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Sergei Trofimovich authored
In Trac #9221 one of problems using high --jobs=<N> is amount of mutator (or GC) threads we crate. We use userspace spinning-and-yielding (see ACQUIRE_SPIN_LOCK) to acess work stealing queues. In case of N-worker-threads > N-CPUs fraction of time when thread holding spin lock gets descheduled by kernel increases. That causes other threads to waste CPU time before giving up CPU. Signed-off-by: Sergei Trofimovich <siarheit@google.com> Test Plan: ghc --make -j8 and -j80 have comparable sys time on a 8-core system. Reviewers: austin, gintas, bgamari, simonmar Reviewed By: bgamari, simonmar Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2482 GHC Trac Issues: #9221
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