A user has ran into a storage performance issue, and it has been traced back to CONFIG_INTEL_IOMMU_DEFAULT_ON being enabled.
They have a Dell XtremIO FC storage server, running VMWare ESXi 7.0U3, with 4x pvscsi controllers (2 LUNs per controller), running a single large LV with 8-way 1MB stripe. There are Ubuntu 20.04 and 22.04 VMs running on the same server. The VMs are attached to the storage unit through iSCSI. When running the following FIO script: [write1] filename=/dev/xio2data/prd01 readwrite=randwrite random_generator=tausworthe64 blocksize=8K ioengine=libaio iodepth=32 direct=1 runtime=30 numjobs=8 group_reporting invalidate=0 On 20.04 with 5.4.0-109-generic they see: WRITE: bw=1010MiB/s (1059MB/s), 1010MiB/s-1010MiB/s (1059MB/s-1059MB/s), io=29.6GiB (31.8GB), run=30007-30007msec They note a 2%-3% %SYS load. On 22.04 with 5.15.0-27-generic they see: WRITE: bw=568MiB/s (595MB/s), 568MiB/s-568MiB/s (595MB/s-595MB/s), io=16.6GiB (17.9GB), run=30007-30007msec They note a consistent 18%-19% %SYS load, and poor performance. It seems VMWare emulates a IOMMU, and their VMs were configuring 8 IOMMU groups for their PCI devices, and it was significantly impacting iSCSI performance. When intel_iommu=off was supplied on the kernel command line, the performance issue is no longer present. This is a suitable workaround for the time being. This user is in agreement with and asking for CONFIG_INTEL_IOMMU_DEFAULT_ON to be disabled. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1971699 Title: disable Intel DMA remapping by default Status in linux package in Ubuntu: Invalid Status in linux source package in Jammy: In Progress Bug description: [Impact] It seems that enabling Intel IOMMU can cause some weird gfx problems, see for example: https://bugs.launchpad.net/bugs/1971146 https://bugs.launchpad.net/bugs/1965882 [Test case] We don't have any specific test case, only other bug reports that tracked down the origin of the issue as being introduced when CONFIG_INTEL_IOMMU_DEFAULT_ON has been enabled by default. [Fix] Revert "UBUNTU: [Config] enable Intel DMA remapping options by default" [Regression potential] DMA remapping device not present at boot by default, users that require this feature will need to specifically add intel_iommu=on to the kernel boot parameters to enable it. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1971699/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
