> On Jan 18, 2021, at 1:00 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> On 2021-01-18 16:18, Chuck Lever wrote:
>>> On Jan 12, 2021, at 9:38 AM, Will Deacon <will@xxxxxxxxxx> wrote:
>>>
>>> [Expanding cc list to include DMA-IOMMU and intel IOMMU folks]
>>>
>>> On Fri, Jan 08, 2021 at 04:18:36PM -0500, Chuck Lever wrote:
>>>> 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.
>> Any thoughts?
>> How about some tools to try or debugging advice? I don't know where to start.
>
> I'm not familiar enough with VT-D internals or Infiniband to have a clue why the middle commit makes any difference (the calculation itself is not on a fast path, so AFAICS the worst it could do is change your maximum DMA address size from 48/57 bits to 47/56, and that seems relatively benign).
Thanks for your response. Understood that you are not responding
about the middle commit (c062db039f40).
However, that's a pretty small and straightforward change, so I've
experimented a bit with that. Commenting out the new code there, I
get some relief:
Children see throughput for 12 initial writers = 4266621.62 kB/sec
Parent sees throughput for 12 initial writers = 4254756.31 kB/sec
Min throughput per process = 354847.75 kB/sec
Max throughput per process = 356167.59 kB/sec
Avg throughput per process = 355551.80 kB/sec
Min xfer = 1044736.00 kB
CPU Utilization: Wall time 2.951 CPU time 1.981 CPU utilization 67.11 %
Children see throughput for 12 rewriters = 4314827.34 kB/sec
Parent sees throughput for 12 rewriters = 4310347.32 kB/sec
Min throughput per process = 358599.72 kB/sec
Max throughput per process = 360319.06 kB/sec
Avg throughput per process = 359568.95 kB/sec
Min xfer = 1043968.00 kB
CPU utilization: Wall time 2.912 CPU time 2.057 CPU utilization 70.62 %
Children see throughput for 12 readers = 4614004.47 kB/sec
Parent sees throughput for 12 readers = 4609014.68 kB/sec
Min throughput per process = 382414.81 kB/sec
Max throughput per process = 388519.50 kB/sec
Avg throughput per process = 384500.37 kB/sec
Min xfer = 1032192.00 kB
CPU utilization: Wall time 2.701 CPU time 1.900 CPU utilization 70.35 %
Children see throughput for 12 re-readers = 4653743.81 kB/sec
Parent sees throughput for 12 re-readers = 4647155.31 kB/sec
Min throughput per process = 384995.69 kB/sec
Max throughput per process = 390874.09 kB/sec
Avg throughput per process = 387811.98 kB/sec
Min xfer = 1032960.00 kB
CPU utilization: Wall time 2.684 CPU time 1.907 CPU utilization 71.06 %
I instrumented the code to show the "before" and "after" values.
The value of domain->domain.geometry.aperture_end on my system
before this commit (and before the c062db039f40 code) is:
144,115,188,075,855,871 = 2^57
The c062db039f40 code sets domain->domain.geometry.aperture_end to:
281,474,976,710,655 = 2^48
Fwiw, this system uses the Intel C612 chipset with Intel(R) Xeon(R)
E5-2603 v3 @ 1.60GHz CPUs.
My sense is that "CPU time" remains about the same because the problem
isn't manifesting as an increase in instruction path length. Wall time
goes up, CPU time stays the same, the ratio of those (ie, utilization)
drops.
--
Chuck Lever
