** Also affects: linux-azure (Ubuntu Jammy)
Importance: Undecided
Status: New
** Changed in: linux-azure (Ubuntu Jammy)
Importance: Undecided => Medium
** Changed in: linux-azure (Ubuntu Jammy)
Status: New => In Progress
** Changed in: linux-azure (Ubuntu Jammy)
Assignee: (unassigned) => Tim Gardner (timg-tpi)
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https://bugs.launchpad.net/bugs/1971701
Title:
Azure: swiotlb patch needed for CVM
Status in linux-azure package in Ubuntu:
New
Status in linux-azure source package in Jammy:
In Progress
Bug description:
SRU Justification
[Impact]
[Azure][CVM] Include the swiotlb patch to increase the disk/network
performance
Description
As we discussed, there will be new CVM-supporting linux-azure kernels that're
based on v5.13 and v5.15. Here I'm requesting the below patch to be included
into the two kernels because it can significantly improve the disk/network
performance:
swiotlb: Split up single swiotlb lock:
https://github.com/intel/tdx/commit/4529b5784c141782c72ec9bd9a92df2b68cb7d45
We have tested the patch with the upstream 5.16-rc8.
BTW, the patch is unlikely to be in the mainline kernel, as the community is
trying to resolve the lock contention issue in the swiotlb code using a
different per-device per-queue implementation, which would need quite some time
to be finalized -- before that happens, we need this out-of-tree patch to
achieve good disk/network performance for CVM GA on Azure.
(BTW, the v5.4-based linux-azure-cvm kernel does not need the patch,
because it uses a private bounce buffer implementation:
drivers/hv/hv_bounce.c, which doesn’t have the I/O performance issue
caused by lock contention in the mainline kernel’s swiotlb code.)
[Test Case]
[Microsoft tested]
I tried the April-27 amd64 test kernel and it worked great for me:
1. The test kernels booted up successfully with 256 virtual CPUs + 100 GB
memory.
2. The kernel worked when I changed the MTU of the NetVSC NIC.
3. The Hyper-V HeartBeat/TimeSync/ShutDown VMBsus devices also worked as
expected.
4. I did some quick disk I/O and network stress tests and found no issue.
When I did the above tests, I changed the low MMIO size to 3GB (which
is the setting for a VM on Azure today) by "set-vm decui-u2004-cvm
-LowMemoryMappedIoSpace 3GB".
Our test team will do more testing, including performance test. We
expect the performance of this v5.15 test kernel should be on par with
the v5.4 linux-azure-cvm kernel.
[Where things could go wrong]
Networking could fail or continue to suffer from poor performance.
[Other Info]
SF: #00332721
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