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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

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ahrens
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@ahrens ahrens commented Jul 23, 2018

External-issue: DLPX-59292

Motivation and Context

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.

Description

We accomplish this by
allowing zio_done() to return a "next zio to execute" to zio_execute().

How Has This Been Tested?

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

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Performance enhancement (non-breaking change which improves efficiency)
  • Code cleanup (non-breaking change which makes code smaller or more readable)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation (a change to man pages or other documentation)

Checklist:

  • My code follows the ZFS on Linux code style requirements.
  • I have updated the documentation accordingly.
  • I have read the contributing document.
  • I have added tests to cover my changes.
  • All new and existing tests passed.
  • All commit messages are properly formatted and contain Signed-off-by.
  • Change has been approved by a ZFS on Linux member.

@ahrens
reduce taskq and context-switch cost of zio pipe
c24e3fe 
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>
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codecov bot commented Jul 24, 2018 •
edited

Codecov Report

Merging #7736 into master will increase coverage by 0.19%.
The diff coverage is 93.75%.

Impacted file tree graph

@@            Coverage Diff             @@
##           master    #7736      +/-   ##
==========================================
+ Coverage   78.08%   78.28%   +0.19%     
==========================================
  Files         368      368              
  Lines      111899   111897       -2     
==========================================
+ Hits        87378    87599     +221     
+ Misses      24521    24298     -223
Flag Coverage Δ
#kernel 78.8% <83.87%> (+0.07%) ⬆️
#user 67.22% <87.5%> (+0.3%) ⬆️

Continue to review full report at Codecov.

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behlendorf
behlendorf approved these changes Jul 26, 2018
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Even ignoring the performance wins from making this change, I think it makes the pipeline code more readable and intuitive. Looks good!

@behlendorf behlendorf added Status: Accepted Ready to integrate (reviewed, tested) Reviewed labels Jul 27, 2018
@ahrens ahrens added the Type: Performance Performance improvement or performance problem label Aug 2, 2018
@behlendorf behlendorf merged commit 6284003 into openzfs:master Aug 2, 2018
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ahrens commented Oct 5, 2018

Let's consider backporting this to 0.7.x, given that it fixes a regression (helps get performance back closer to 0.6). See #7834 for details.

@tonyhutter tonyhutter added this to To do in 0.7.12 Oct 8, 2018
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@ahrens I had the same thought. Alternately, we should be able to just revert the __zio_execute() -> zio_taskq_dispatch() hunk in zio_notify_parent() which would be a much smaller change.

3dfb57a#diff-bdeb26c3e7b126b07c42b8583f57a2b9R517

behlendorf pushed a commit to behlendorf/zfs that referenced this pull request Oct 10, 2018
@ahrens @behlendorf
Reduce taskq and context-switch cost of zio pipe
b1d1d21 
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).

Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: George Wilson <george.wilson@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-59292
Closes openzfs#7736
behlendorf pushed a commit to behlendorf/zfs that referenced this pull request Oct 10, 2018
@ahrens @behlendorf
Reduce taskq and context-switch cost of zio pipe
496657a 
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).

Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: George Wilson <george.wilson@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-59292
Requires-spl: spl-0.7-release
Closes openzfs#7736
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Opened PR #8011, it applied relatively cleanly so I ported the entire patch.

@tonyhutter tonyhutter moved this from To do to In progress in 0.7.12 Oct 26, 2018
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Oct 31, 2018
@ahrens @tonyhutter
Reduce taskq and context-switch cost of zio pipe
8e1d0d3 
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).

Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: George Wilson <george.wilson@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-59292
Closes openzfs#7736
tonyhutter pushed a commit that referenced this pull request Nov 13, 2018
@ahrens @tonyhutter
Reduce taskq and context-switch cost of zio pipe
45579c9 
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).

Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: George Wilson <george.wilson@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-59292
Closes #7736
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