> > echo 400000 > /sys/module/kvm/parameters/halt_poll_ns
Tried this change by itself first. CPU was noticeably lower on all cores, almost never exceeding 70% The stuttering effect however was much worse. Next, you have a quad-core+threads processor and you're creating a > quad-core+threads VM; where's the hypervisor supposed to run? Of > course you're going to get stutters when the guest vCPU is preempted by > the hypervisor or another system process. Be less aggressive in > allocating vCPUs, virtualization isn't free. Try a 3-core+threads VM > for example. Tried 3 cores vs 4 as suggested: "-smp 6,sockets=1,cores=3,threads=2" Guest consistently locks up during boot. No idea what is up with that :/ Went all the way down to 2 cores next: "-smp 4,sockets=1,cores=2,threads=2" 3.11% slower than native now by 3Dmark test, but all my static/jitter issues are totally gone! Will have to continue with the other tuning you suggested to find a sweet spot in-between the two extremes, but now I know I am only dealing with CPU starving and not something more complex. Thanks. On Sun, May 8, 2016 at 9:34 PM, Alex Williamson <alex.william...@redhat.com> wrote: > On Sun, 8 May 2016 19:22:43 -0700 > "Lance R. Vick" <la...@lrvick.net> wrote: > > > I have some persistent issues with a couple USB devices via vfio/qemu > that > > I do not experience when booted native: > > > > Oculus Rift CV1 > > - head-tracking stutter (any game or demo) > > - host CPU ~100% on every core (any game or demo) > > - at same time Guest CPU may only show ~20% usage > > - audio static from built-in USB DAC > > > > FiiO K1 USB Headphone DAC/AMP > > - mild but noticeable cuts/jitter > > > > This may also impact other USB devices in ways I have not yet noticed. > Any > > kind of test to quantify this would be helpful. Guest OS was installed > on a > > dedicated disk so I can easily native boot to compare tests when needed. > > > > 3DMark score is only 0.64% lower in VM which indicates to me at least > > things are -mostly- there: > > http://www.3dmark.com/compare/fs/8402818/fs/8403766 > > > > Guest OS is Windows 10 Professional. > > > > Any advice/debugging tips would be most welcome. > > > > Here are all the other relevant details I can think of for my setup: > > For starters, turn down the kvm module parameter halt_poll_ns to > something like 400000 to see if that brings the host CPU usage down. > > echo 400000 > /sys/module/kvm/parameters/halt_poll_ns > > Kernel v4.4.8 already includes a change to make this the default. > > Next, you have a quad-core+threads processor and you're creating a > quad-core+threads VM; where's the hypervisor supposed to run? Of > course you're going to get stutters when the guest vCPU is preempted by > the hypervisor or another system process. Be less aggressive in > allocating vCPUs, virtualization isn't free. Try a 3-core+threads VM > for example. > > Pinning vCPUs can also reduce stutter, it helps to avoid cold caches > and avoids resource conflicts that can occur with threads. Switch to > libvirt, it makes this easy. > > Pinning the emulator can help to make sure it doesn't run on a > conflicting CPU to a vCPU. Libvirt makes this easy to manage. > > Tune irqbalanced to avoid placing interrupts on CPUs used by vCPUs. > > Finally, if you're willing to dedicate CPUs completely to the VM, use > the isolcpus= and nohz_full= boot options to avoid the scheduler > running anything on the physical CPUs except for the vCPUs. > > > > > sudo qemu-system-x86_64 \ > > -enable-kvm \ > > -machine type=q35,accel=kvm \ > > -cpu host,kvm=off \ > > Enable hyper-v extensions, but specify the hv_vendor_id option to avoid > Code43 issues. Some workloads can have huge benefits from this, things > like 3dmark are mostly unaffected. > > > -smp 8,sockets=1,cores=4,threads=2 \ > > -m 8G \ > > -mem-path /dev/hugepages \ > > -device virtio-scsi-pci,id=scsi \ > > -drive file=/dev/sda,id=disk,format=raw,if=none \ > > -device scsi-hd,drive=disk \ > > -device vfio-pci,host=01:00.0,multifunction=on,x-vga=on \ > > x-vga=on isn't needed when you're booting the VM with OVMF. > multifunction=on doesn't do anything useful unless you also specify and > addr= option for the devices. > > > -device vfio-pci,host=01:00.1 \ > > -drive > if=pflash,format=raw,readonly,file=/usr/share/edk2.git/ovmf-x64/OVMF_CODE-pure-efi.fd > > \ > > -drive if=pflash,format=raw,file=/tmp/OVMF_VARS-pure-efi.fd \ > > -nographic \ > > -vga none \ > > -usb \ > > -device vfio-pci,host=00:14.0 \ > > -rtc clock=host,base=utc > > > > > > -- Lance R. Vick
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