Re: [PATCH v2 0/6] musb: Improve performance for hub-attached webcams

[Matwey V. Kornilov]

ÐÑ, 2 ÐÑÐ. 2019 Ð. Ð 20:33, Bin Liu <b-liu@xxxxxx>:
>
> Matwey,
>
> On Tue, Jul 02, 2019 at 08:29:03PM +0300, Matwey V. Kornilov wrote:
> > Ping?
>
> I was offline and just got back. I will review it soon. Sorry for the
> delay.

Ping?

>
> -Bin.
>
> >
> > ÐÑ, 14 ÐÑÐ. 2019 Ð. Ð 19:47, Matwey V. Kornilov <matwey@xxxxxxxxxx>:
> > >
> > > The series is concerned to issues with isochronous transfer while
> > > streaming the USB webcam data. I discovered the issue first time
> > > when attached PWC USB webcam to AM335x-based BeagleBone Black SBC.
> > > It appeared that the root issue was in numerous missed IN requests
> > > during isochronous transfer where each missing leaded to the frame
> > > drop. Since every IN request is triggered in MUSB driver
> > > individually, it is important to queue the send IN request as
> > > earlier as possible when the previous IN completed. At the same
> > > time the URB giveback handler of the device driver has also to be
> > > called there, that leads to arbitrarily delay depending on the
> > > device driver performance. The details with the references are
> > > described in [1].
> > >
> > > The issue has two parts:
> > >
> > >   1) peripheral driver URB callback performance
> > >   2) MUSB host driver performance
> > >
> > > It appeared that the first part is related to the wrong memory
> > > allocation strategy in the most USB webcam drivers. Non-cached
> > > memory is used in assumption that coherent DMA memory leads to
> > > the better performance than non-coherent memory in conjunction with
> > > the proper synchronization. Yet the assumption might be valid for
> > > x86 platforms some time ago, the issue was fixed for PWC driver in:
> > >
> > >     1161db6776bd ("media: usb: pwc: Don't use coherent DMA buffers for ISO transfer")
> > >
> > > that leads to 3.5x performance gain. The more generic fix for this
> > > common issue are coming for the rest drivers [2].
> > >
> > > The patch allowed successfully running full-speed USB PWC webcams
> > > attached directly to BeagleBone Black USB port.
> > >
> > > However, the second part of the issue is still present for
> > > peripheral device attached through the high-speed USB hub due to
> > > its 125us frame time. The patch series is intended to reorganize
> > > musb_advance_schedule() to allow host to send IN request quicker.
> > >
> > > The patch series is organized as the following. First three patches
> > > improve readability of the existing code in
> > > musb_advance_schedule(). Patches 4 and 5 introduce updated
> > > signature for musb_start_urb(). The last patch introduce new
> > > code-path in musb_advance_schedule() which allows for faster
> > > response.
> > >
> > > References:
> > >
> > > [1] https://www.spinics.net/lists/linux-usb/msg165735.html
> > > [2] https://www.spinics.net/lists/linux-media/msg144279.html
> > >
> > > Changes since v1:
> > >  - Patch 6 was redone to keep URB giveback order and stop transmission at
> > >    erroneous URB.
> > >
> > > Matwey V. Kornilov (6):
> > >   usb: musb: Use USB_DIR_IN when calling musb_advance_schedule()
> > >   usb: musb: Introduce musb_qh_empty() helper function
> > >   usb: musb: Introduce musb_qh_free() helper function
> > >   usb: musb: Rename musb_start_urb() to musb_start_next_urb()
> > >   usb: musb: Introduce musb_start_urb()
> > >   usb: musb: Decrease URB starting latency in musb_advance_schedule()
> > >
> > >  drivers/usb/musb/musb_host.c | 132 ++++++++++++++++++++++++++++---------------
> > >  drivers/usb/musb/musb_host.h |   1 +
> > >  2 files changed, 86 insertions(+), 47 deletions(-)
> > >
> > > --
> > > 2.16.4
> > >
> >
> >
> > --
> > With best regards,
> > Matwey V. Kornilov



-- 
With best regards,
Matwey V. Kornilov