This bug is awaiting verification that the linux-azure/5.15.0-1006.7 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-jammy' to 'verification-done-jammy'. If the problem still exists, change the tag 'verification-needed-jammy' to 'verification-failed-jammy'.
If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you! ** Tags added: verification-needed-jammy -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux-azure in Ubuntu. https://bugs.launchpad.net/bugs/1972662 Title: [Azure] PCI: hv: Do not set PCI_COMMAND_MEMORY to reduce VM boot time Status in linux-azure package in Ubuntu: Fix Released Status in linux-azure source package in Focal: Fix Committed Status in linux-azure source package in Impish: Fix Committed Status in linux-azure source package in Jammy: Fix Committed Bug description: SRU Justification [Impact] A VM on Azure can have 14 GPUs, and each GPU may have a huge MMIO BAR, e.g. 128 GB. Currently the boot time of such a VM can be 4+ minutes, and most of the time is used by the host to unmap/map the vBAR from/to pBAR when the VM clears and sets the PCI_COMMAND_MEMORY bit: each unmap/map operation for a 128GB BAR needs about 1.8 seconds, and the pci-hyperv driver and the Linux PCI subsystem flip the PCI_COMMAND_MEMORY bit eight times (see pci_setup_device() -> pci_read_bases() and pci_std_update_resource()), increasing the boot time by 1.8 * 8 = 14.4 seconds per GPU, i.e. 14.4 * 14 = 201.6 seconds in total. Fix the slowness by not turning on the PCI_COMMAND_MEMORY in pci-hyperv.c, so the bit stays in the off state before the PCI device driver calls pci_enable_device(): when the bit is off, pci_read_bases() and pci_std_update_resource() don't cause Hyper-V to unmap/map the vBARs. With this change, the boot time of such a VM is reduced by 1.8 * (8-1) * 14 = 176.4 seconds. [Test Case] Microsoft tested [Where things could go wrong] PCI BAR setup could fail or be incorrect. [Other Info] SF: #00336342 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-azure/+bug/1972662/+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
