Move write aggregation memory copy out of vq_lock #8890
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Memory copy is too heavy operation to do under the congested lock. Moving it out reduces congestion by many times to almost invisible. Since the original zio removed from the queue, and the child zio is not executed yet, I don't see why would the copy need protection. My guess it just remained like this from the time when lock was not dropped here, which was added later to fix lock ordering issue. Multi-threaded sequential write tests with both HDD and SSD pools with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major reduction of lock congestion, saving from 15% to 35% of CPU time and increasing throughput from 10% to 40%. Signed-off-by: Alexander Motin <mav@FreeBSD.org>
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@ahrens @behlendorf You've touched this code before, what do you think? Any objections? |
behlendorf
approved these changes
Jun 12, 2019
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Great timing, I happened to be looking at contention on this same lock. I agree, as long as the vdev_queue_io_remove operation is kept under the lock it's safe to move the copy itself outside.
Related to this I suggest also taking a look at the vdev_queue_io_{add,remove} and vdev_queue_pending_{add,remove} functions. They're called under the same queue lock but may end up blocked on a per-pool kstat lock. This doesn't currently appear to be a major bottleneck, but clearly isn't a good thing.
ahrens
approved these changes
Jun 12, 2019
In FreeBSD's native ZFS those parts are commented out as illumos'isms. That is why I don't see them in profiler. I can imagine pool-wide lock at those places must be terrible under high IOPS. |
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per pool and per objset kstats can be aggsummed eliminating their locks altogether |
Codecov Report
@@ Coverage Diff @@
## master #8890 +/- ##
==========================================
+ Coverage 78.64% 78.7% +0.06%
==========================================
Files 382 382
Lines 117808 117808
==========================================
+ Hits 92645 92719 +74
+ Misses 25163 25089 -74
Continue to review full report at Codecov.
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tonyhutter
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Aug 13, 2019
Memory copy is too heavy operation to do under the congested lock. Moving it out reduces congestion by many times to almost invisible. Since the original zio removed from the queue, and the child zio is not executed yet, I don't see why would the copy need protection. My guess it just remained like this from the time when lock was not dropped here, which was added later to fix lock ordering issue. Multi-threaded sequential write tests with both HDD and SSD pools with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major reduction of lock congestion, saving from 15% to 35% of CPU time and increasing throughput from 10% to 40%. Reviewed-by: Richard Yao <ryao@gentoo.org> Reviewed-by: Matt Ahrens <mahrens@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes openzfs#8890
tonyhutter
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Aug 22, 2019
Memory copy is too heavy operation to do under the congested lock. Moving it out reduces congestion by many times to almost invisible. Since the original zio removed from the queue, and the child zio is not executed yet, I don't see why would the copy need protection. My guess it just remained like this from the time when lock was not dropped here, which was added later to fix lock ordering issue. Multi-threaded sequential write tests with both HDD and SSD pools with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major reduction of lock congestion, saving from 15% to 35% of CPU time and increasing throughput from 10% to 40%. Reviewed-by: Richard Yao <ryao@gentoo.org> Reviewed-by: Matt Ahrens <mahrens@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes openzfs#8890
tonyhutter
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Aug 23, 2019
Memory copy is too heavy operation to do under the congested lock. Moving it out reduces congestion by many times to almost invisible. Since the original zio removed from the queue, and the child zio is not executed yet, I don't see why would the copy need protection. My guess it just remained like this from the time when lock was not dropped here, which was added later to fix lock ordering issue. Multi-threaded sequential write tests with both HDD and SSD pools with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major reduction of lock congestion, saving from 15% to 35% of CPU time and increasing throughput from 10% to 40%. Reviewed-by: Richard Yao <ryao@gentoo.org> Reviewed-by: Matt Ahrens <mahrens@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes openzfs#8890
tonyhutter
pushed a commit
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Sep 17, 2019
Memory copy is too heavy operation to do under the congested lock. Moving it out reduces congestion by many times to almost invisible. Since the original zio removed from the queue, and the child zio is not executed yet, I don't see why would the copy need protection. My guess it just remained like this from the time when lock was not dropped here, which was added later to fix lock ordering issue. Multi-threaded sequential write tests with both HDD and SSD pools with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major reduction of lock congestion, saving from 15% to 35% of CPU time and increasing throughput from 10% to 40%. Reviewed-by: Richard Yao <ryao@gentoo.org> Reviewed-by: Matt Ahrens <mahrens@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes openzfs#8890
tonyhutter
pushed a commit
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Sep 18, 2019
Memory copy is too heavy operation to do under the congested lock. Moving it out reduces congestion by many times to almost invisible. Since the original zio removed from the queue, and the child zio is not executed yet, I don't see why would the copy need protection. My guess it just remained like this from the time when lock was not dropped here, which was added later to fix lock ordering issue. Multi-threaded sequential write tests with both HDD and SSD pools with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major reduction of lock congestion, saving from 15% to 35% of CPU time and increasing throughput from 10% to 40%. Reviewed-by: Richard Yao <ryao@gentoo.org> Reviewed-by: Matt Ahrens <mahrens@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes openzfs#8890
tonyhutter
pushed a commit
that referenced
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Sep 26, 2019
Memory copy is too heavy operation to do under the congested lock. Moving it out reduces congestion by many times to almost invisible. Since the original zio removed from the queue, and the child zio is not executed yet, I don't see why would the copy need protection. My guess it just remained like this from the time when lock was not dropped here, which was added later to fix lock ordering issue. Multi-threaded sequential write tests with both HDD and SSD pools with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major reduction of lock congestion, saving from 15% to 35% of CPU time and increasing throughput from 10% to 40%. Reviewed-by: Richard Yao <ryao@gentoo.org> Reviewed-by: Matt Ahrens <mahrens@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes #8890
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Motivation and Context
Memory copy is too heavy operation to do under the congested lock.
Moving it out reduces congestion by many times to almost invisible.
Since the original zio removed from the queue, and the child zio is
not executed yet, I don't see why would the copy need protection.
My guess it just remained like this from the time when lock was not
dropped here, which was added later to fix lock ordering issue.
Description
How Has This Been Tested?
I've tested this patch of FreeBSD head on dual-socket Xeon 4110.
Sequential write to 12 ZVOLs on both HDD and SSD striped pools
with ZVOL block sizes of 4KB, 16KB, 64KB and 128KB all show major
reduction of lock congestion, saving from 15% to 35% of CPU time
and increasing throughput from 10% to 40%.
Types of changes
Checklist:
Signed-off-by.