Re: [PATCH 3/5] usb: gadget: uvc: increase worker prio to WQ_HIGHPRI

[Dan Vacura <w36195@motorola.com>]

Hi Michael,

Thanks for this change it improves the performance with the DWC3
controller on QCOM chips in an Android 5.10 kernel. I haven't tested the
scatter/gather path, so memcpy was used here via
uvc_video_encode_isoc(). I was able to get around 30% improvement (fps
on host side). I did modify the alloc to only set the WQ_HIGHPRI flag.

On Tue, Apr 19, 2022 at 11:46:57PM +0300, Laurent Pinchart wrote:
> Hi Michael,
> 
> Thank you for the patch.
> 
> On Sun, Apr 03, 2022 at 01:39:12AM +0200, Michael Grzeschik wrote:
> > Likewise to the uvcvideo hostside driver, this patch is changing the
> > simple workqueue to an async_wq with higher priority. This ensures that
> > the worker will not be scheduled away while the video stream is handled.
> > 
> > Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> > +	video->async_wq = alloc_workqueue("uvcvideo", WQ_UNBOUND | WQ_HIGHPRI, 0);
> 
> Unless I'm mistaken, an unbound work queue means that multiple CPUs will
> handle tasks in parallel. Is that safe ?

I found that with the WQ_UNBOUND flag I didn't see any performance
improvement to the baseline, perhaps related to cpu caching or
scheduling delays. I didn't notice any stability problems or concurrent
execution. Do you see any benefit to keeping the WQ_UNBOUND flag?

> 
> > +	if (!video->async_wq)
> > +		return -EINVAL;
> 
> -- 
> Regards,
> 
> Laurent Pinchart

Thanks,

Dan