On Thu, May 11, 2023 at 08:44:27AM -0700, Reinette Chatre wrote: > > Qemu allocates interrupts incrementally at the time the guest unmasks an > interrupt, for example each time a Linux guest runs request_irq(). > > Dynamic allocation of MSI-X interrupts was not possible until v6.2 [1]. > This prompted Qemu to, when allocating a new interrupt, first release all > previously allocated interrupts (including disable of MSI-X) followed > by re-allocation of all interrupts that includes the new interrupt. > Please see [2] for a detailed discussion about this issue. > > Releasing and re-allocating interrupts may be acceptable if all > interrupts are unmasked during device initialization. If unmasking of > interrupts occur during runtime this may result in lost interrupts. > For example, consider an accelerator device with multiple work queues, > each work queue having a dedicated interrupt. A work queue can be > enabled at any time with its associated interrupt unmasked while other > work queues are already active. Having all interrupts released and MSI-X > disabled to enable the new work queue will impact active work queues. > > This series builds on the recent interrupt sub-system core changes > that added support for dynamic MSI-X allocation after initial MSI-X > enabling. > > Add support for dynamic MSI-X allocation to vfio-pci. A flag > indicating lack of support for dynamic allocation already exist: > VFIO_IRQ_INFO_NORESIZE and has always been set for MSI and MSI-X. With > support for dynamic MSI-X the flag is cleared for MSI-X when supported, > enabling Qemu to modify its behavior. > > Any feedback is appreciated Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Jason
