[bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node

Thu Jul 22 03:05:00 PDT 2021

On 22/07/2021 08:58, Ming Lei wrote:
> On Wed, Jul 21, 2021 at 12:07:22PM +0100, John Garry wrote:
>> On 21/07/2021 10:59, Ming Lei wrote:
>>>> I have now removed that from the tree, so please re-pull.
>>> Now the kernel can be built successfully, but not see obvious improvement
>>> on the reported issue:
>>>
>>> [root at ampere-mtjade-04 ~]# uname -a
>>> Linux ampere-mtjade-04.khw4.lab.eng.bos.redhat.com 5.14.0-rc2_smmu_fix+ #2 SMP Wed Jul 21 05:49:03 EDT 2021 aarch64 aarch64 aarch64 GNU/Linux
>>>
>>> [root at ampere-mtjade-04 ~]# taskset -c 0 ~/git/tools/test/nvme/io_uring 10 1 /dev/nvme1n1 4k
>>> + fio --bs=4k --ioengine=io_uring --fixedbufs --registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 --iodepth_batch_complete_min=16 --filename=/dev/nvme1n1 --direct=1 --runtime=10 --numjobs=1 --rw=randread --name=test --group_reporting
>>> test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=io_uring, iodepth=64
>>> fio-3.27
>>> Starting 1 process
>>> Jobs: 1 (f=1): [r(1)][100.0%][r=1503MiB/s][r=385k IOPS][eta 00m:00s]
>>> test: (groupid=0, jobs=1): err= 0: pid=3143: Wed Jul 21 05:58:14 2021
>>>     read: IOPS=384k, BW=1501MiB/s (1573MB/s)(14.7GiB/10001msec)
>> I am not sure what baseline you used previously, but you were getting 327K
>> then, so at least this would be an improvement.
> Looks the improvement isn't from your patches, please see the test result on
> v5.14-rc2:
> 
> [root at ampere-mtjade-04 ~]# uname -a
> Linux ampere-mtjade-04.khw4.lab.eng.bos.redhat.com 5.14.0-rc2_linus #3 SMP Thu Jul 22 03:41:24 EDT 2021 aarch64 aarch64 aarch64 GNU/Linux
> [root at ampere-mtjade-04 ~]# taskset -c 0 ~/git/tools/test/nvme/io_uring 20 1 /dev/nvme1n1 4k
> + fio --bs=4k --ioengine=io_uring --fixedbufs --registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 --iodepth_batch_complete_min=16 --filename=/dev/nvme1n1 --direct=1 --runtime=20 --numjobs=1 --rw=randread --name=test --group_reporting
> test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=io_uring, iodepth=64
> fio-3.27
> Starting 1 process
> Jobs: 1 (f=1): [r(1)][100.0%][r=1489MiB/s][r=381k IOPS][eta 00m:00s]
> test: (groupid=0, jobs=1): err= 0: pid=3099: Thu Jul 22 03:53:04 2021
>    read: IOPS=381k, BW=1487MiB/s (1559MB/s)(29.0GiB/20001msec)

I'm a bit surprised at that.

Anyway, I don't see such an issue as you are seeing on my system. In 
general, running from different nodes doesn't make a huge difference. 
But note that the NVMe device is on NUMA node #2 on my 4-node system. I 
assume that the IOMMU is also located in that node.

sudo taskset -c 0 fio/fio --bs=4k --ioengine=io_uring --fixedbufs 
--registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 
--iodepth_batch_complete_min=16 --filename=/dev/nvme0n1 --direct=1 
--runtime=20 --numjobs=1 --rw=randread --name=test --group_reporting

  read: IOPS=479k

---
sudo taskset -c 4 fio/fio --bs=4k --ioengine=io_uring --fixedbufs 
--registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 
--iodepth_batch_complete_min=16 --filename=/dev/nvme0n1 --direct=1 
--runtime=20 --numjobs=1 --rw=randread --name=test --group_reporting

  read: IOPS=307k

---
sudo taskset -c 32 fio/fio --bs=4k --ioengine=io_uring --fixedbufs 
--registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 
--iodepth_batch_complete_min=16 --filename=/dev/nvme0n1 --direct=1 
--runtime=20 --numjobs=1 --rw=randread --name=test --group_reporting

read: IOPS=566k

--
sudo taskset -c 64 fio/fio --bs=4k --ioengine=io_uring --fixedbufs 
--registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 
--iodepth_batch_complete_min=16 --filename=/dev/nvme0n1 --direct=1 
--runtime=20 --numjobs=1 --rw=randread --name=test --group_reporting

read: IOPS=488k

---
sudo taskset -c 96 fio/fio --bs=4k --ioengine=io_uring --fixedbufs 
--registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 
--iodepth_batch_complete_min=16 --filename=/dev/nvme0n1 --direct=1 
--runtime=20 --numjobs=1 --rw=randread --name=test --group_reporting

  read: IOPS=508k

If you check below, you can see that cpu4 services an NVMe irq. From 
checking htop, during the test that cpu is at 100% load, which I put the 
performance drop (vs cpu0) down to.

Here's some system info:

HW queue irq affinities:
PCI name is 81:00.0: nvme0n1
-eirq 298, cpu list 67, effective list 67
-eirq 299, cpu list 32-38, effective list 35
-eirq 300, cpu list 39-45, effective list 39
-eirq 301, cpu list 46-51, effective list 46
-eirq 302, cpu list 52-57, effective list 52
-eirq 303, cpu list 58-63, effective list 60
-eirq 304, cpu list 64-69, effective list 68
-eirq 305, cpu list 70-75, effective list 70
-eirq 306, cpu list 76-80, effective list 76
-eirq 307, cpu list 81-85, effective list 84
-eirq 308, cpu list 86-90, effective list 86
-eirq 309, cpu list 91-95, effective list 92
-eirq 310, cpu list 96-101, effective list 100
-eirq 311, cpu list 102-107, effective list 102
-eirq 312, cpu list 108-112, effective list 108
-eirq 313, cpu list 113-117, effective list 116
-eirq 314, cpu list 118-122, effective list 118
-eirq 315, cpu list 123-127, effective list 124
-eirq 316, cpu list 0-5, effective list 4
-eirq 317, cpu list 6-11, effective list 6
-eirq 318, cpu list 12-16, effective list 12
-eirq 319, cpu list 17-21, effective list 20
-eirq 320, cpu list 22-26, effective list 22
-eirq 321, cpu list 27-31, effective list 28

john at ubuntu:~$ lscpu | grep NUMA
NUMA node(s):  4
NUMA node0 CPU(s):   0-31
NUMA node1 CPU(s):   32-63
NUMA node2 CPU(s):   64-95
NUMA node3 CPU(s):   96-127

john at ubuntu:~$ lspci | grep -i non
81:00.0 Non-Volatile memory controller: Huawei Technologies Co., Ltd. 
Device 0123 (rev 45)

cat /sys/block/nvme0n1/device/device/numa_node
2

[   52.968495] nvme 0000:81:00.0: Adding to iommu group 5
[   52.980484] nvme nvme0: pci function 0000:81:00.0
[   52.999881] nvme nvme0: 23/0/0 default/read/poll queues
[   53.019821]  nvme0n1: p1

john at ubuntu:~$ uname -a
Linux ubuntu 5.14.0-rc2-dirty #297 SMP PREEMPT Thu Jul 22 09:23:33 BST 
2021 aarch64 aarch64 aarch64 GNU/Linux

Thanks,
John