On 2021-01-22 16:18, Chuck Lever wrote:
On Jan 21, 2021, at 10:00 PM, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:
+Isaac
On 1/22/21 3:09 AM, Chuck Lever wrote:
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).
With the last commit, though, at least part of it is likely to be the unfortunate inevitable overhead of the internal indirection through the IOMMU API. There's a coincidental performance-related thread where we've already started pondering some ideas in that area[1] (note that Intel is the last one to the party here; AMD has been using this path for a while, and it's all that arm64 systems have ever known). I'm not sure if there's any difference in the strict invalidation behaviour between the IOMMU API calls and the old intel_dma_ops, but I suppose that might be worth quickly double-checking as well. I guess the main thing would be to do some profiling to see where time is being spent in iommu-dma and intel-iommu vs. just different parts of intel-iommu before, and whether anything in particular stands out beyond the extra call overhead currently incurred by iommu_{map,unmap}.
I did a function_graph trace of the above iozone test on a v5.10 NFS
client and again on v5.11-rc. There is a substantial timing difference
in dma_map_sg_attrs. Each excerpt below is for DMA-mapping a 120KB set
of pages that are part of an NFS/RDMA WRITE operation.
v5.10:
1072.028308: funcgraph_entry: | dma_map_sg_attrs() {
1072.028308: funcgraph_entry: | intel_map_sg() {
1072.028309: funcgraph_entry: | find_domain() {
1072.028309: funcgraph_entry: 0.280 us | get_domain_info();
1072.028310: funcgraph_exit: 0.930 us | }
1072.028310: funcgraph_entry: 0.360 us | domain_get_iommu();
1072.028311: funcgraph_entry: | intel_alloc_iova() {
1072.028311: funcgraph_entry: | alloc_iova_fast() {
1072.028311: funcgraph_entry: 0.375 us | _raw_spin_lock_irqsave();
1072.028312: funcgraph_entry: 0.285 us | __lock_text_start();
1072.028313: funcgraph_exit: 1.500 us | }
1072.028313: funcgraph_exit: 2.052 us | }
1072.028313: funcgraph_entry: | domain_mapping() {
1072.028313: funcgraph_entry: | __domain_mapping() {
1072.028314: funcgraph_entry: 0.350 us | pfn_to_dma_pte();
1072.028315: funcgraph_entry: 0.942 us | domain_flush_cache();
1072.028316: funcgraph_exit: 2.852 us | }
1072.028316: funcgraph_entry: 0.275 us | iommu_flush_write_buffer();
1072.028317: funcgraph_exit: 4.213 us | }
1072.028318: funcgraph_exit: 9.392 us | }
1072.028318: funcgraph_exit: + 10.073 us | }
1072.028323: xprtrdma_mr_map: mr.id=115 nents=30 122880@0xe476ca03f1180000:0x18011105 (TO_DEVICE)
1072.028323: xprtrdma_chunk_read: task:63879@5 pos=148 122880@0xe476ca03f1180000:0x18011105 (more)
v5.11-rc:
57.602990: funcgraph_entry: | dma_map_sg_attrs() {
57.602990: funcgraph_entry: | iommu_dma_map_sg() {
57.602990: funcgraph_entry: 0.285 us | iommu_get_dma_domain();
57.602991: funcgraph_entry: 0.270 us | iommu_dma_deferred_attach();
57.602991: funcgraph_entry: | iommu_dma_sync_sg_for_device() {
57.602992: funcgraph_entry: 0.268 us | dev_is_untrusted();
57.602992: funcgraph_exit: 0.815 us | }
57.602993: funcgraph_entry: 0.267 us | dev_is_untrusted();
57.602993: funcgraph_entry: | iommu_dma_alloc_iova() {
57.602994: funcgraph_entry: | alloc_iova_fast() {
57.602994: funcgraph_entry: 0.260 us | _raw_spin_lock_irqsave();
57.602995: funcgraph_entry: 0.293 us | _raw_spin_lock();
57.602995: funcgraph_entry: 0.273 us | _raw_spin_unlock_irqrestore();
57.602996: funcgraph_entry: 1.147 us | alloc_iova();
57.602997: funcgraph_exit: 3.370 us | }
57.602997: funcgraph_exit: 3.945 us | }
57.602998: funcgraph_entry: 0.272 us | dma_info_to_prot();
57.602998: funcgraph_entry: | iommu_map_sg_atomic() {
57.602998: funcgraph_entry: | __iommu_map_sg() {
57.602999: funcgraph_entry: 1.733 us | __iommu_map();
57.603001: funcgraph_entry: 1.642 us | __iommu_map();
57.603003: funcgraph_entry: 1.638 us | __iommu_map();
57.603005: funcgraph_entry: 1.645 us | __iommu_map();
57.603007: funcgraph_entry: 1.630 us | __iommu_map();
57.603009: funcgraph_entry: 1.770 us | __iommu_map();
57.603011: funcgraph_entry: 1.730 us | __iommu_map();
57.603013: funcgraph_entry: 1.633 us | __iommu_map();
57.603015: funcgraph_entry: 1.605 us | __iommu_map();
57.603017: funcgraph_entry: 2.847 us | __iommu_map();
57.603020: funcgraph_entry: 2.847 us | __iommu_map();
57.603024: funcgraph_entry: 2.955 us | __iommu_map();
57.603027: funcgraph_entry: 2.928 us | __iommu_map();
57.603030: funcgraph_entry: 2.933 us | __iommu_map();
57.603034: funcgraph_entry: 2.943 us | __iommu_map();
57.603037: funcgraph_entry: 2.928 us | __iommu_map();
57.603040: funcgraph_entry: 2.857 us | __iommu_map();
57.603044: funcgraph_entry: 2.953 us | __iommu_map();
57.603047: funcgraph_entry: 3.023 us | __iommu_map();
57.603050: funcgraph_entry: 1.645 us | __iommu_map();
57.603052: funcgraph_exit: + 53.648 us | }
57.603052: funcgraph_exit: + 54.178 us | }
57.603053: funcgraph_exit: + 62.953 us | }
57.603053: funcgraph_exit: + 63.567 us | }
57.603059: xprtrdma_mr_map: task:60@5 mr.id=4 nents=30 122880@0xd79cc0e2f18c0000:0x00010501 (TO_DEVICE)
57.603060: xprtrdma_chunk_read: task:60@5 pos=148 122880@0xd79cc0e2f18c0000:0x00010501 (more)
I kind of believe it's due to the indirect calls. This is also reported
on ARM.
https://lore.kernel.org/linux-iommu/1610376862-927-1-git-send-email-isaacm@xxxxxxxxxxxxxx/
Maybe we can try changing indirect calls to static ones to verify this
problem.
I liked the idea of map_sg() enough to try my hand at building a PoC for
Intel, based on Isaac's patch series. It's just a cut-and-paste of the
generic iommu.c code with the indirect calls to ops->map() replaced.
The indirect calls do not seem to be the problem. Calling intel_iommu_map
directly appears to be as costly as calling it indirectly.
However, perhaps there are other ways map_sg() can be beneficial. In
v5.10, __domain_mapping and iommu_flush_write_buffer() appear to be
invoked just once for each large map operation, for example.
Oh, if the driver needs to do maintenance beyond just installing PTEs,
that should probably be devolved to iotlb_sync_map anyway. There's a
patch series here generalising that to be more useful, which is
hopefully just waiting to be merged now:
https://lore.kernel.org/linux-iommu/20210107122909.16317-1-yong.wu@xxxxxxxxxxxx/
Robin.
Here's a trace of my prototype in operation:
380.620150: funcgraph_entry: | iommu_dma_map_sg() {
380.620150: funcgraph_entry: 0.285 us | iommu_get_dma_domain();
380.620150: funcgraph_entry: 0.265 us | iommu_dma_deferred_attach();
380.620151: funcgraph_entry: | iommu_dma_sync_sg_for_device() {
380.620151: funcgraph_entry: 0.285 us | dev_is_untrusted();
380.620152: funcgraph_exit: 0.860 us | }
380.620152: funcgraph_entry: 0.263 us | dev_is_untrusted();
380.620153: funcgraph_entry: | iommu_dma_alloc_iova() {
380.620153: funcgraph_entry: | alloc_iova_fast() {
380.620153: funcgraph_entry: 0.268 us | _raw_spin_lock_irqsave();
380.620154: funcgraph_entry: 0.275 us | _raw_spin_unlock_irqrestore();
380.620155: funcgraph_exit: 1.402 us | }
380.620155: funcgraph_exit: 1.955 us | }
380.620155: funcgraph_entry: 0.265 us | dma_info_to_prot();
380.620156: funcgraph_entry: | iommu_map_sg_atomic() {
380.620156: funcgraph_entry: | __iommu_map_sg() {
380.620156: funcgraph_entry: | intel_iommu_map_sg() {
380.620157: funcgraph_entry: 0.270 us | iommu_pgsize();
380.620157: funcgraph_entry: | intel_iommu_map() {
380.620157: funcgraph_entry: 0.970 us | __domain_mapping();
380.620159: funcgraph_entry: 0.265 us | iommu_flush_write_buffer();
380.620159: funcgraph_exit: 2.322 us | }
380.620160: funcgraph_entry: 0.270 us | iommu_pgsize();
380.620160: funcgraph_entry: | intel_iommu_map() {
380.620161: funcgraph_entry: 0.957 us | __domain_mapping();
380.620162: funcgraph_entry: 0.275 us | iommu_flush_write_buffer();
380.620163: funcgraph_exit: 2.315 us | }
380.620163: funcgraph_entry: 0.265 us | iommu_pgsize();
380.620163: funcgraph_entry: | intel_iommu_map() {
380.620164: funcgraph_entry: 0.940 us | __domain_mapping();
380.620165: funcgraph_entry: 0.270 us | iommu_flush_write_buffer();
380.620166: funcgraph_exit: 2.295 us | }
....
380.620247: funcgraph_entry: 0.262 us | iommu_pgsize();
380.620248: funcgraph_entry: | intel_iommu_map() {
380.620248: funcgraph_entry: 0.935 us | __domain_mapping();
380.620249: funcgraph_entry: 0.305 us | iommu_flush_write_buffer();
380.620250: funcgraph_exit: 2.315 us | }
380.620250: funcgraph_entry: 0.273 us | iommu_pgsize();
380.620251: funcgraph_entry: | intel_iommu_map() {
380.620251: funcgraph_entry: 0.967 us | __domain_mapping();
380.620253: funcgraph_entry: 0.265 us | iommu_flush_write_buffer();
380.620253: funcgraph_exit: 2.310 us | }
380.620254: funcgraph_exit: + 97.388 us | }
380.620254: funcgraph_exit: + 97.960 us | }
380.620254: funcgraph_exit: + 98.482 us | }
380.620255: funcgraph_exit: ! 105.175 us | }
380.620260: xprtrdma_mr_map: task:1607@5 mr.id=126 nents=30 122880@0xf06ee5bbf1920000:0x70011104 (TO_DEVICE)
380.620261: xprtrdma_chunk_read: task:1607@5 pos=148 122880@0xf06ee5bbf1920000:0x70011104 (more)
--
Chuck Lever
