Re: [PATCH v4 0/6] Asynchronous UVC

[Mauro Carvalho Chehab <mchehab+samsung@kernel.org>]

Em Tue, 15 May 2018 21:19:50 +0100
Kieran Bingham <kieran.bingham@ideasonboard.com> escreveu:

> Hi Mauro,
> 
> On 15/05/18 20:22, Mauro Carvalho Chehab wrote:
> > Em Tue, 27 Mar 2018 17:45:57 +0100
> > Kieran Bingham <kieran.bingham@ideasonboard.com> escreveu:
> >   
> >> The Linux UVC driver has long provided adequate performance capabilities for
> >> web-cams and low data rate video devices in Linux while resolutions were low.
> >>
> >> Modern USB cameras are now capable of high data rates thanks to USB3 with
> >> 1080p, and even 4k capture resolutions supported.
> >>
> >> Cameras such as the Stereolabs ZED (bulk transfers) or the Logitech BRIO
> >> (isochronous transfers) can generate more data than an embedded ARM core is
> >> able to process on a single core, resulting in frame loss.
> >>
> >> A large part of this performance impact is from the requirement to
> >> ‘memcpy’ frames out from URB packets to destination frames. This unfortunate
> >> requirement is due to the UVC protocol allowing a variable length header, and
> >> thus it is not possible to provide the target frame buffers directly.
> >>
> >> Extra throughput is possible by moving the actual memcpy actions to a work
> >> queue, and moving the memcpy out of interrupt context thus allowing work tasks
> >> to be scheduled across multiple cores.
> >>
> >> This series has been tested on both the ZED and BRIO cameras on arm64
> >> platforms, and with thanks to Randy Dunlap, a Dynex 1.3MP Webcam, a Sonix USB2
> >> Camera, and a built in Toshiba Laptop camera, and with thanks to Philipp Zabel
> >> for testing on a Lite-On internal Laptop Webcam, Logitech C910 (USB2 isoc),
> >> Oculus Sensor (USB3 isoc), and Microsoft HoloLens Sensors (USB3 bulk).
> >>
> >> As far as I am aware iSight devices, and devices which use UVC to encode data
> >> (output device) have not yet been tested - but should find no ill effect (at
> >> least not until they are tested of course :D )
> >>
> >> Tested-by: Randy Dunlap <rdunlap@infradead.org>
> >> Tested-by: Philipp Zabel <philipp.zabel@gmail.com>
> >>
> >> v2:
> >>  - Fix race reported by Guennadi
> >>
> >> v3:
> >>  - Fix similar race reported by Laurent
> >>  - Only queue work if required (encode/isight do not queue work)
> >>  - Refactor/Rename variables for clarity
> >>
> >> v4:
> >>  - (Yet another) Rework of the uninitialise path.
> >>    This time to hopefully clean up the shutdown races for good.
> >>    use usb_poison_urb() to halt all URBs, then flush the work queue
> >>    before freeing.
> >>  - Rebase to latest linux-media/master  
> > 
> > Kieran/Laurent,
> > 
> > What's the status of this patchset?  
> 
> I believe v4 was my final version (until someone tells me otherwise), and fixed
> all known races. Unless there has been bitrot since I posted  (was last rebased
> at v4.16-rc4 ?) ...
> 
> It would be good to at least get it in -next for a while if not mainline...
> 
> Laurent ?
> 
> The latest version is available in a branch at :
>   git://git.kernel.org/pub/scm/linux/kernel/git/kbingham/rcar.git uvc/async/v4
> 
> Let me know if I need to post a rebased version.

From my side, if there are just minor conflicts, no need to rebase, but
Laurent should ack if I'm willing to pick from your git tree. If he
acks, please send a pull request with git pull-request. Both patchwork
regex parser and my scripts rely on the exact format produced by git.

Regards,
Mauro