El 18 oct. 2017 8:53 p. m., "Alex Williamson" <alex.william...@redhat.com> escribió
As of kernel v4.12, Legacy KVM device assignment has been removed from the kernel (it had previously been deprecated), so I suggest to start with migrating your configuration to using vfio-pci instead. You can find vfio documentation in the Linux kernel tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/ linux.git/tree/Documentation/vfio.txt In my blog: http://vfio.blogspot.com/ And various other places. Regarding interrupt behavior, without additional hardware assistance, assigned device interrupts are handled by the host kernel and injected into the guest. This does not generally incur much load on the host since the interrupt is simply forwarded and not serviced at the device in the host. Usually the problem here is the additional latency, which is one of the more notable overheads when using device assignment. Various processor offloads can help to alleviate this. Intel first introduced APICv, which among other things, allows interrupts to be injected into the VM via IPI without incurring a vm-exit. To take advantage of this, you'd want a) hardware supporting APICv and b) redirect the physical interrupt to a host processor not running a vCPU such that the interrupt itself doesn't trigger a world switch. The kvm_intel module has an enable_apicv option, if you can't enable it, as seen in /sys/module/kvm_intel/parameters/enable_apicv, then your hardware doesn't support it. Newer yet Intel hardware supports posted interrupts, which allows interrupts to be injected directly into the VM, bypassing the host entirely. This one is even trickier to setup AIUI the interrupt needs to arrive to the pCPU while it's running the vCPU to which the interrupt is directed in the VM. I'm not entirely sure how to test for this support, but unless you're running pretty recent Xeon E5+ processors, it's probably safe to assume it's not there. When you say recent Xeon E5+, you mean, for example Xeon E5-2650-v4 processor? The above optimizations also assume that you're using a modern device which supports nicely aligned MMIO mapped registers and MSI or MSI/X interrupts. If you're using a device that requires INTx or makes use of I/O port registers, or interacts with PCI config space of the device on each interrupt, or perhaps even if you're using an old OS in the VM that flips MSI mask bits regularly, most of those actions require hypervisor interaction and will reduce the performance and increase the overhead of the device. Thanks, Alex _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://www.redhat.com/mailman/listinfo/vfio-users Greetings
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