linux-kernel - Re: [PATCH v2 0/3] uvc gadget performance issues

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Date:   Tue, 11 Oct 2022 21:53:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Michael Grzeschik <mgr@...gutronix.de>
Cc:     Dan Vacura <w36195@...orola.com>, linux-usb@...r.kernel.org,
        Daniel Scally <dan.scally@...asonboard.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Jonathan Corbet <corbet@....net>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Felipe Balbi <balbi@...nel.org>,
        Paul Elder <paul.elder@...asonboard.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 0/3] uvc gadget performance issues

On Tue, Oct 11, 2022 at 09:48:08PM +0200, Michael Grzeschik wrote:
> I also have an patch in the queue that will limit the sg support for
> devices with speed > HIGH_SPEED. Because of the overhead of the limited
> transfer payload of 1024*3 Bytes, it is possible that a simple memcpy
> will actually be fast enough. But for that patch I still have to make
> proper measurements. Btw. which USB speed are you transferring with?

For a payload that small, yes a memcpy is almost always faster.  I think
it's only much larger sizes that actually start to help with sg.

Can you submit this change now?  Odds are it will help out a lot of
systems.

thanks,

greg k-h