a004338372
Authored by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: Dan Kimmel <dan.kimmel@delphix.com> Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com> Reviewed by: Prashanth Sreenivasa <pks@delphix.com> Approved by: Robert Mustacchi <rm@joyent.com> Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> 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. Porting Notes: - The error handling for when dbuf_read_impl() fails which was originally added in commit 5f6d0b6f5 has been preserved. OpenZFS-issue: https://www.illumos.org/issues/8025 OpenZFS-commit: https://github.com/openzfs/openzfs/commit/8ec5c7c Closes #6048
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