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reduce taskq and context-switch cost of zio pipe #7736

Merged
merged 1 commit into from
Aug 2, 2018
Merged

reduce taskq and context-switch cost of zio pipe #7736

merged 1 commit into from
Aug 2, 2018

Commits on Jul 23, 2018

  1. reduce taskq and context-switch cost of zio pipe 

    When doing a read from disk, ZFS creates 3 ZIO's: a zio_null(), the
logical zio_read(), and then a physical zio. Currently, each of these
results in a separate taskq_dispatch(zio_execute).

On high-read-iops workloads, this causes a significant performance
impact. By processing all 3 ZIO's in a single taskq entry, we reduce the
overhead on taskq locking and context switching.  We accomplish this by
allowing zio_done() to return a "next zio to execute" to zio_execute().

This results in a ~12% performance increase for random reads, from
96,000 iops to 108,000 iops (with recordsize=8k, on SSD's).

External-issue: DLPX-59292
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
    @ahrens
    ahrens committed Jul 23, 2018
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