illumos/illumos-gate@d28671a3b0d28671a3b0https://www.illumos.org/issues/8373
The code that writes ZIL blocks uses dmu_tx_assign(TXG_WAIT) to assign
a transaction to a transaction group. That seems to be logically
incorrect as writing of the ZIL block does not introduce any new dirty
data. Also, when there is a lot of dirty data, the call can introduce
significant delays into the ZIL commit path, thus affecting all
synchronous writes. Additionally, ARC throttling may affect the ZIL
writing.
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Approved by: Dan McDonald <danmcd@joyent.com>
Author: Andriy Gapon <avg@FreeBSD.org>
MFC after: 2 weeks
984d43cca5