Andriy Gapon 1c42c71f38 8025 dbuf_read() creates unnecessary zio_root() for bonus buf
illumos/illumos-gate@def4fac588
def4fac588

https://www.illumos.org/issues/8025
  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%.

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>
Author: Matthew Ahrens <mahrens@delphix.com>
2017-05-26 11:29:31 +00:00
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