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From:   "Matwey V. Kornilov" <matwey.kornilov@gmail.com>
Date:   Wed, 23 Oct 2019 11:12:29 +0300
Message-ID: <CAJs94EYv4TUDm-J+9ToGccGC-hMQ1XU12DZYUmQVdfdjL5PBPg@mail.gmail.com>
Subject: Re: [PATCH v2 0/6] musb: Improve performance for hub-attached webcams
To:     Bin Liu <b-liu@ti.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        "open list:MUSB MULTIPOINT HIGH SPEED DUAL-ROLE CONTROLLER" 
        <linux-usb@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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=D0=BF=D0=BD, 9 =D1=81=D0=B5=D0=BD=D1=82. 2019 =D0=B3. =D0=B2 19:33, Matwey=
 V. Kornilov <matwey.kornilov@gmail.com>:
>
> =D0=B2=D1=82, 2 =D0=B8=D1=8E=D0=BB. 2019 =D0=B3. =D0=B2 20:33, Bin Liu <b=
-liu@ti.com>:
> >
> > 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?
>

Ping?

> >
> > -Bin.
> >
> > >
> > > =D0=BF=D1=82, 14 =D0=B8=D1=8E=D0=BD. 2019 =D0=B3. =D0=B2 19:47, Matwe=
y V. Kornilov <matwey@sai.msu.ru>:
> > > >
> > > > 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 transmiss=
ion 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


--=20
With best regards,
Matwey V. Kornilov