I just had a look at the Ubuntu kernel noble master-next tree and can find
commit:
"Revert "s390: update defconfigs"" under the hash b2b97a62f055
and I can see that it got reverted with that:
$ git show b2b97a62f055 | grep CONFIG_IOMMU_DEFAULT_DMA_STRICT
CONFIG_IOMMU_DEFAULT_DMA_STRICT option needs to be disabled.
-CONFIG_IOMMU_DEFAULT_DMA_STRICT=y
-CONFIG_IOMMU_DEFAULT_DMA_STRICT=y
But git also tells me that it is in since kernel v6.8 and with that since the
first ubuntu 6.8 kernel we had: Ubuntu-6.8.0-6 -- so should also be in
Ubuntu-6.8.0-31.
But it does not seem to be reflected in the kernel options of the Ubuntu kernel:
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 24.04 LTS
Release: 24.04
Codename: noble
$ uname -a
Linux hwe0008 6.8.0-31-generic #31-Ubuntu SMP Sat Apr 20 00:14:26 UTC 2024
s390x s390x s390x GNU/Linux
$ grep CONFIG_IOMMU_DEFAULT_DMA_STRICT /boot/config-6.8.0-31-generic
CONFIG_IOMMU_DEFAULT_DMA_STRICT=y
also not in the current, updated kernel:
Linux hwe0008 6.8.0-36-generic #36-Ubuntu SMP Mon Jun 10 09:59:13 UTC 2024
s390x s390x s390x GNU/Linux
$ grep CONFIG_IOMMU_DEFAULT_DMA_STRICT /boot/config-6.8.0-31-generic
CONFIG_IOMMU_DEFAULT_DMA_STRICT=y
For some reason the change in the upstream commit was not taken over into the
Ubuntu kernel configs ...
** Changed in: ubuntu-z-systems
Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)
** Changed in: linux (Ubuntu)
Assignee: Skipper Bug Screeners (skipper-screen-team) => (unassigned)
** Changed in: ubuntu-z-systems
Importance: Undecided => High
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https://bugs.launchpad.net/bugs/2071471
Title:
[UBUNTU 24.04] IOMMU DMA mode changed in kernel config causes massive
throughput degradation for PCI-related network workloads
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