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
