performance regression noted in v5.11-rc after c062db039f40

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Hi-

[ Please cc: me on replies, I'm not currently subscribed to
iommu@lists ].

I'm running NFS performance tests on InfiniBand using CX-3 Pro cards
at 56Gb/s. The test is iozone on an NFSv3/RDMA mount:

/home/cel/bin/iozone -M -+u -i0 -i1 -s1g -r256k -t12 -I

For those not familiar with the way storage protocols use RDMA, The
initiator/client sets up memory regions and the target/server uses
RDMA Read and Write to move data out of and into those regions. The
initiator/client uses only RDMA memory registration and invalidation
operations, and the target/server uses RDMA Read and Write.

My NFS client is a two-socket 12-core x86_64 system with its I/O MMU
enabled using the kernel command line options "intel_iommu=on
iommu=strict".

Recently I've noticed a significant (25-30%) loss in NFS throughput.
I was able to bisect on my client to the following commits.

Here's 65f746e8285f ("iommu: Add quirk for Intel graphic devices in
map_sg"). This is about normal for this test.

	Children see throughput for 12 initial writers 	= 4732581.09 kB/sec
 	Parent sees throughput for 12 initial writers 	= 4646810.21 kB/sec
 	Min throughput per process 			=  387764.34 kB/sec
 	Max throughput per process 			=  399655.47 kB/sec
 	Avg throughput per process 			=  394381.76 kB/sec
 	Min xfer 					= 1017344.00 kB
 	CPU Utilization: Wall time    2.671    CPU time    1.974    CPU utilization  73.89 %
 	Children see throughput for 12 rewriters 	= 4837741.94 kB/sec
 	Parent sees throughput for 12 rewriters 	= 4833509.35 kB/sec
 	Min throughput per process 			=  398983.72 kB/sec
 	Max throughput per process 			=  406199.66 kB/sec
 	Avg throughput per process 			=  403145.16 kB/sec
 	Min xfer 					= 1030656.00 kB
 	CPU utilization: Wall time    2.584    CPU time    1.959    CPU utilization  75.82 %
 	Children see throughput for 12 readers 		= 5921370.94 kB/sec
 	Parent sees throughput for 12 readers 		= 5914106.69 kB/sec
 	Min throughput per process 			=  491812.38 kB/sec
 	Max throughput per process 			=  494777.28 kB/sec
 	Avg throughput per process 			=  493447.58 kB/sec
 	Min xfer 					= 1042688.00 kB
 	CPU utilization: Wall time    2.122    CPU time    1.968    CPU utilization  92.75 %
 	Children see throughput for 12 re-readers 	= 5947985.69 kB/sec
 	Parent sees throughput for 12 re-readers 	= 5941348.51 kB/sec
 	Min throughput per process 			=  492805.81 kB/sec
 	Max throughput per process 			=  497280.19 kB/sec
 	Avg throughput per process 			=  495665.47 kB/sec
 	Min xfer 					= 1039360.00 kB
 	CPU utilization: Wall time    2.111    CPU time    1.968    CPU utilization  93.22 %

Here's c062db039f40 ("iommu/vt-d: Update domain geometry in
iommu_ops.at(de)tach_dev"). It's losing some steam here.

	Children see throughput for 12 initial writers 	= 4342419.12 kB/sec
 	Parent sees throughput for 12 initial writers 	= 4310612.79 kB/sec
 	Min throughput per process 			=  359299.06 kB/sec
 	Max throughput per process 			=  363866.16 kB/sec
 	Avg throughput per process 			=  361868.26 kB/sec
 	Min xfer 					= 1035520.00 kB
 	CPU Utilization: Wall time    2.902    CPU time    1.951    CPU utilization  67.22 %
 	Children see throughput for 12 rewriters 	= 4408576.66 kB/sec
 	Parent sees throughput for 12 rewriters 	= 4404280.87 kB/sec
 	Min throughput per process 			=  364553.88 kB/sec
 	Max throughput per process 			=  370029.28 kB/sec
 	Avg throughput per process 			=  367381.39 kB/sec
 	Min xfer 					= 1033216.00 kB
 	CPU utilization: Wall time    2.836    CPU time    1.956    CPU utilization  68.97 %
 	Children see throughput for 12 readers 		= 5406879.47 kB/sec
 	Parent sees throughput for 12 readers 		= 5401862.78 kB/sec
 	Min throughput per process 			=  449583.03 kB/sec
 	Max throughput per process 			=  451761.69 kB/sec
 	Avg throughput per process 			=  450573.29 kB/sec
 	Min xfer 					= 1044224.00 kB
 	CPU utilization: Wall time    2.323    CPU time    1.977    CPU utilization  85.12 %
 	Children see throughput for 12 re-readers 	= 5410601.12 kB/sec
 	Parent sees throughput for 12 re-readers 	= 5403504.40 kB/sec
 	Min throughput per process 			=  449918.12 kB/sec
 	Max throughput per process 			=  452489.28 kB/sec
 	Avg throughput per process 			=  450883.43 kB/sec
 	Min xfer 					= 1043456.00 kB
 	CPU utilization: Wall time    2.321    CPU time    1.978    CPU utilization  85.21 %

And here's c588072bba6b ("iommu/vt-d: Convert intel iommu driver to
the iommu ops"). Significant throughput loss.

	Children see throughput for 12 initial writers 	= 3812036.91 kB/sec
 	Parent sees throughput for 12 initial writers 	= 3753683.40 kB/sec
 	Min throughput per process 			=  313672.25 kB/sec
 	Max throughput per process 			=  321719.44 kB/sec
 	Avg throughput per process 			=  317669.74 kB/sec
 	Min xfer 					= 1022464.00 kB
 	CPU Utilization: Wall time    3.309    CPU time    1.986    CPU utilization  60.02 %
 	Children see throughput for 12 rewriters 	= 3786831.94 kB/sec
 	Parent sees throughput for 12 rewriters 	= 3783205.58 kB/sec
 	Min throughput per process 			=  313654.44 kB/sec
 	Max throughput per process 			=  317844.50 kB/sec
 	Avg throughput per process 			=  315569.33 kB/sec
 	Min xfer 					= 1035520.00 kB
 	CPU utilization: Wall time    3.302    CPU time    1.945    CPU utilization  58.90 %
 	Children see throughput for 12 readers 		= 4265828.28 kB/sec
 	Parent sees throughput for 12 readers 		= 4261844.88 kB/sec
 	Min throughput per process 			=  352305.00 kB/sec
 	Max throughput per process 			=  357726.22 kB/sec
 	Avg throughput per process 			=  355485.69 kB/sec
 	Min xfer 					= 1032960.00 kB
 	CPU utilization: Wall time    2.934    CPU time    1.942    CPU utilization  66.20 %
 	Children see throughput for 12 re-readers 	= 4220651.19 kB/sec
 	Parent sees throughput for 12 re-readers 	= 4216096.04 kB/sec
 	Min throughput per process 			=  348677.16 kB/sec
 	Max throughput per process 			=  353467.44 kB/sec
 	Avg throughput per process 			=  351720.93 kB/sec
 	Min xfer 					= 1035264.00 kB
 	CPU utilization: Wall time    2.969    CPU time    1.952    CPU utilization  65.74 %

The regression appears to be 100% reproducible. 


--
Chuck Lever







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