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dbeb879699
dmu_object_alloc() is single-threaded, so when multiple threads are creating files in a single filesystem, they spend a lot of time waiting for the os_obj_lock. To improve performance of multi-threaded file creation, we must make dmu_object_alloc() typically not grab any filesystem-wide locks. The solution is to have a "next object to allocate" for each CPU. Each of these "next object"s is in a different block of the dnode object, so that concurrent allocation holds dnodes in different dbufs. When a thread's "next object" reaches the end of a chunk of objects (by default 4 blocks worth -- 128 dnodes), it will be reset to the per-objset os_obj_next, which will be increased by a chunk of objects (128). Only when manipulating the os_obj_next will we need to grab the os_obj_lock. This decreases lock contention dramatically, because each thread only needs to grab the os_obj_lock briefly, once per 128 allocations. This results in a 70% performance improvement to multi-threaded object creation (where each thread is creating objects in its own directory), from 67,000/sec to 115,000/sec, with 8 CPUs. Work sponsored by Intel Corp. Authored by: Matthew Ahrens <mahrens@delphix.com> Reviewed-by: Ned Bass <bass6@llnl.gov> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Ported-by: Matthew Ahrens <mahrens@delphix.com> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> OpenZFS-issue: https://www.illumos.org/issues/8199 OpenZFS-commit: https://github.com/openzfs/openzfs/pull/374 Closes #4703 Closes #6117 |
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