[linux-dvb] Hardware pid filters: are they worth it?

Michael Krufky mkrufky at linuxtv.org
Fri Nov 21 18:34:38 CET 2008

On Fri, Nov 21, 2008 at 12:28 PM, Devin Heitmueller
<devin.heitmueller at gmail.com> wrote:
> Hello,
> I am doing some driver work, and the USB device I am working on has
> hardware pid filter support.
> Obviously if I don't implement such support, the kernel will do the
> pid filtering.
> Does anyone have any experience with hardware pid filters, and have
> they provided any signficant/visible benefit over the kernel pid
> filter (either from a performance perspective or power consumption)?
> This is aside from the known benefit that some streams would fit into
> a full speed USB whereas before you might have required high speed
> without the hardware pid filter.
> It's probably a good thing to implement in general for completeness,
> but if there isn't any power or performance savings then I'm not sure
> it's worth my time.
> Opinions welcome,
> Devin

With the powerful systems around in this day & age, the gain of using
hardware PID filters is hardly noticeable.

Then again, you like to tweak things to the ultimate flexibility, and
this is a good case for tweaking.

While a system with a single usb2 stick will not be taxed at all by
software PID filtering, there might be a slight performance
enhancement in a system with 7 or 8 usb2 sticks using hardware PID
filters rather than software.

On the other hand, a device with hardware PID filters can be used on a
USB1.1 port, which would normally not provide enough bandwidth for
full transport using software filtering.

So yes, there is a gain in using hardware PID filters, but 90% of the
users would never notice the difference.


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