Slow video output from webcam with qemu-xhci but smooth with usb-ehci

Slow video output from webcam with qemu-xhci but smooth with usb-ehci

[Diego Viola]

Hi,

I'm experiencing a lot of choppiness in the video output when I pass
through my USB webcam to the guest using qemu-xhci as follows:

qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
-device qemu-xhci,id=xhci -device
usb-host,bus=xhci.0,hostdevice=/dev/bus/usb/002/004

My webcam is:

Bus 002 Device 004: ID 04f2:b449 Chicony Electronics Co., Ltd Integrated Camera

I am using mpv /dev/video0 from the guest.

It works fine if I use usb-ehci instead, e.g.:

qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
-device usb-ehci,id=ehci -device
usb-host,bus=ehci.0,hostdevice=/dev/bus/usb/002/004

In this case, the video output from mpv /dev/video0 is not choppy.

My QEMU version is 5.2.0 -- I am running Arch Linux on the host and guest.

Any ideas please?

Thanks,
Diego

Re: Slow video output from webcam with qemu-xhci but smooth with usb-ehci

[Diego Viola]

Not sure it's related but I'm seeing this on the guest now when I use
mpv --vo=drm on a tty:

[ 28.918606] xhci_hcd 0000:00:04.0: ERROR Transfer event TRB DMA ptr
not part of current TD ep_index 2 comp_code 13
[ 28.919816] xhci_hcd 0000:00:04.0: Looking for event-dma
000000012a8c7d80 trb-start 000000012a8c7d70 trb-end 000000012a8c7d70
seg-start 000000012a8c7000 seg-end 000000012a8c7ff0
[ 28.919818] xhci_hcd 0000:00:04.0: ERROR Transfer event TRB DMA ptr
not part of current TD ep_index 2 comp_code 13
[ 28.921019] xhci_hcd 0000:00:04.0: Looking for event-dma
000000012a8c7d90 trb-start 000000012a8c7d70 trb-end 000000012a8c7d70
seg-start 000000012a8c7000 seg-end 000000012a8c7ff0
[ 28.921023] xhci_hcd 0000:00:04.0: ERROR Transfer event TRB DMA ptr
not part of current TD ep_index 2 comp_code 13
[ 28.922203] xhci_hcd 0000:00:04.0: Looking for event-dma
000000012a8c7da0 trb-start 000000012a8c7d70 trb-end 000000012a8c7d70
seg-start 000000012a8c7000 seg-end 000000012a8c7ff0

Video is then a bit smoother.

Diego

On Sat, Dec 12, 2020 at 1:28 PM Diego Viola <diego.viola@gmail.com> wrote:
>
> Hi,
>
> I'm experiencing a lot of choppiness in the video output when I pass
> through my USB webcam to the guest using qemu-xhci as follows:
>
> qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
> -device qemu-xhci,id=xhci -device
> usb-host,bus=xhci.0,hostdevice=/dev/bus/usb/002/004
>
> My webcam is:
>
> Bus 002 Device 004: ID 04f2:b449 Chicony Electronics Co., Ltd Integrated Camera
>
> I am using mpv /dev/video0 from the guest.
>
> It works fine if I use usb-ehci instead, e.g.:
>
> qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
> -device usb-ehci,id=ehci -device
> usb-host,bus=ehci.0,hostdevice=/dev/bus/usb/002/004
>
> In this case, the video output from mpv /dev/video0 is not choppy.
>
> My QEMU version is 5.2.0 -- I am running Arch Linux on the host and guest.
>
> Any ideas please?
>
> Thanks,
> Diego

Re: Slow video output from webcam with qemu-xhci but smooth with usb-ehci

[Diego Viola]

On Sun, Dec 13, 2020 at 4:30 PM Diego Viola <diego.viola@gmail.com> wrote:
>
> Not sure it's related but I'm seeing this on the guest now when I use
> mpv --vo=drm on a tty:

mpv --vo=drm /dev/video0

Re: Slow video output from webcam with qemu-xhci but smooth with usb-ehci

[Diego Viola]

On Sat, Dec 12, 2020 at 1:28 PM Diego Viola <diego.viola@gmail.com> wrote:
>
> Hi,
>
> I'm experiencing a lot of choppiness in the video output when I pass
> through my USB webcam to the guest using qemu-xhci as follows:
>
> qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
> -device qemu-xhci,id=xhci -device
> usb-host,bus=xhci.0,hostdevice=/dev/bus/usb/002/004
>
> My webcam is:
>
> Bus 002 Device 004: ID 04f2:b449 Chicony Electronics Co., Ltd Integrated Camera
>
> I am using mpv /dev/video0 from the guest.
>
> It works fine if I use usb-ehci instead, e.g.:
>
> qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
> -device usb-ehci,id=ehci -device
> usb-host,bus=ehci.0,hostdevice=/dev/bus/usb/002/004
>
> In this case, the video output from mpv /dev/video0 is not choppy.
>
> My QEMU version is 5.2.0 -- I am running Arch Linux on the host and guest.
>
> Any ideas please?
>
> Thanks,
> Diego

OK, I just noticed that it's mostly at the beginning (when I first run
mpv) that the video is jerky/choppy, looks like mpv is still buffering
at that stage, after buffering gets to 99% the video is smoother (with
xhci).

Now I don't understand why buffering with ehci happens a lot faster/smoother.

Nevermind, not an issue after all.

Diego

Re: Slow video output from webcam with qemu-xhci but smooth with usb-ehci

[Dr. David Alan Gilbert]

* Diego Viola (diego.viola@gmail.com) wrote:
> On Sat, Dec 12, 2020 at 1:28 PM Diego Viola <diego.viola@gmail.com> wrote:
> >
> > Hi,
> >
> > I'm experiencing a lot of choppiness in the video output when I pass
> > through my USB webcam to the guest using qemu-xhci as follows:
> >
> > qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
> > -device qemu-xhci,id=xhci -device
> > usb-host,bus=xhci.0,hostdevice=/dev/bus/usb/002/004
> >
> > My webcam is:
> >
> > Bus 002 Device 004: ID 04f2:b449 Chicony Electronics Co., Ltd Integrated Camera
> >
> > I am using mpv /dev/video0 from the guest.
> >
> > It works fine if I use usb-ehci instead, e.g.:
> >
> > qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
> > -device usb-ehci,id=ehci -device
> > usb-host,bus=ehci.0,hostdevice=/dev/bus/usb/002/004
> >
> > In this case, the video output from mpv /dev/video0 is not choppy.
> >
> > My QEMU version is 5.2.0 -- I am running Arch Linux on the host and guest.
> >
> > Any ideas please?
> >
> > Thanks,
> > Diego
> 
> OK, I just noticed that it's mostly at the beginning (when I first run
> mpv) that the video is jerky/choppy, looks like mpv is still buffering
> at that stage, after buffering gets to 99% the video is smoother (with
> xhci).
> 
> Now I don't understand why buffering with ehci happens a lot faster/smoother.

I don't understand it either; but cc'ing in Gerd for his USB wisdom.

Dave

> Nevermind, not an issue after all.
> 
> Diego
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK