linux-kernel - Re: [PATCH v3 2/6] usb: dwc3: gadget: cancel requests instead of release after missed isoc

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Message-ID: <20221020205308.GA6319@qjv001-XeonWs>
Date:   Thu, 20 Oct 2022 15:53:10 -0500
From:   Jeff Vanhoof <jdv1029@...il.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     Jeffrey Vanhoof <jvanhoof@...orola.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "corbet@....net" <corbet@....net>,
        "dan.scally@...asonboard.com" <dan.scally@...asonboard.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "m.grzeschik@...gutronix.de" <m.grzeschik@...gutronix.de>,
        "paul.elder@...asonboard.com" <paul.elder@...asonboard.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Dan Vacura <W36195@...orola.com>
Subject: Re: [PATCH v3 2/6] usb: dwc3: gadget: cancel requests instead of
 release after missed isoc

Hi Thinh,

> On Wed, Oct 19, 2022 at 11:06:08PM +0000, Thinh Nguyen wrote:
> > Hi,
> >

<snip>

> > > 
> > > > The logic to detect underrun doesn't trigger because the queued list is
> > > > always non-empty, but the queued requests are expected to be missed
> > > > already. So you keep seeing missed isoc.
> > > > 
> > > > There are a few things you can mitigate this issue:
> > > > 1) Don't set IMI if the request indicates no_interrupt. This reduces the
> > > >    time software needs to handle interrupts.
> > > 
> > > 
> > > > 2) Improve the underrun detection logic.
> > > 
> > > 
> > > > 3) Increase the queuing frequency from the uvc to keep the request queue
> > > >    full. Note that reduce/avoid setting no_interrupt will allow the
> > > >    controller driver to update uvc often to keep requeuing new requests.
> > > > 
> > > > Best option is 3), but maybe we can do all 3.
> > > >
> > >

I forgot about your option 2. Will start looking into it.

Thanks,
Jeff