Re: [PATCH] USB: host: ehci: allow tine of highspeed nak-count

[Ben Dooks]

On 14/11/18 18:47, Alan Stern wrote:
> On Wed, 14 Nov 2018, Ben Dooks wrote:
>
> > From: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>
> >
> > At least some systems benefit with less scheduling if the NAK count
> > value is set higher than the default 4. For instance a Tegra3 with
> > an SMSC9512 showed less interrupt load when this was changed to 14.
>
> Interesting.  Why do you think this is?  In theory, increasing the NAK
> count RL value should cause a higher memory bus load and perhaps a
> slight rise in the interrupt load (transfers will complete a little
> more quickly because the controller tries harder to poll the endpoints
> and see if they are ready).

I thought the NAK counter was decremented until the transfer is given
up on. I'm going to have to go back and get some actual figures from
a running system as this was originally done over a year ago with the
SMSC9512 (IIRC) network driver.

> > To allow the changing of this value, add a sysfs node to each of
> > the controllers to allow run-time changing.
> >
> > Signed-off-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>
>
> The patch looks okay to me.

I'll look at getting some tracing from the SMSC driver to see what
is going on.


--
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

https://www.codethink.co.uk/privacy.html