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Brian Behlendorf
b0319c1faa
dbuf_read() creates a zio_root() to track and wait for all the zio's that may happen as part of this call. However, if the blkptr_t for this buffer is NULL or a hole, we will not create any more zio's, so this zio_root() is unnecessary. This is always the case when calling dbuf_read() on a bonus buffer, because it has no blkptr (it's part of the containing dnode). For workloads that read a lot of bonus buffers (e.g. file creation and removal), creating and destroying these unnecessary zio's can decrease performance by around 3%. The fix is to only create/destroy the zio_root() in dbuf_read() if the blkptr is not NULL and not a hole. Changes sponsored by Intel Corp. Authored by: Matthew Ahrens <mahrens@delphix.com> Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com> Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue openzfs/openzfs#137 Closes #4803 Closes #5382