ACK: [PATCH 0/4][jammy/linux-azure] swiotlb patch needed for CVM

[Bartlomiej Zolnierkiewicz]

Acked-by: Bartlomiej Zolnierkiewicz <bartlomiej.zolnierkiewicz at canonical.com>

On Thu, May 5, 2022 at 2:40 PM Tim Gardner <tim.gardner at canonical.com> wrote:
>
> BugLink: https://bugs.launchpad.net/bugs/1971701
>
> 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