[PATCH] TX algorithms, missetting IFF_OACTIVE and if_timer

[Ruslan Ermilov]

On Fri, Apr 02, 2004 at 09:03:02AM -0800, Bill Paul wrote:
[...]
> > To differentiate the case of an empty
> > ring from the full ring, some drivers (ste(4), dc(4), and
> > nge(4)) have the threshold (6 for dc(4), 3 for ste(4), and
> > 2 for nge(4)) to assert the gap between producer and consumer,
> > thus not allow the producer to catch the consumer.  (The
> > vr(4) is hairier, and I will not discuss it in detail here.)
> > 
> > First, could you please explain these magic numbers?
> 
> Not really, no. Very often, values were chosen because they worked
> (and in some cases, they weren't chosen by me).
> 
Hmm, well, at least I now know (learned the hard way) why the
gap is ever necessary -- I will just silently join the crew
who keep this secret, and don't tell it to anyone.  ;)

> > Also, some drivers use indexes for consumer and producer,
> > where they could use "next" pointers, which should be faster.
> 
> "Should" be faster? I'm not saying you're wrong, but can you prove
> that it's faster to use lists? I started out using linked lists
> for descriptors, but then I started to encounter chips that used
> producer/consumer indexes internally (like the Adaptec 'starfire'
> chip and the Tigon II). I decided that since I tended to allocate
> all of the descriptors in contiguous chunks anyway, it was simpler
> to just treat them as arrays and use index counters.
> 
I experimented with ste(4) today -- except for getting 200 bytes
less driver code when converting to use the precomputed pointers,
I didn't notice any change in performance, so I threw my changes
away.  ;)

> > I also think that using the gap between producer/consumer is
> > suboptimal, but this gap is part of the existing algorithm.
> 
> Nowhere is it written that you can't change the algorithm. :)
> 
Now I know (I wish you'd tell me it) why the gap is necessary,
but let's keep this secret.  ;)

> Note that if you're looking for approval from me to check in these
> patches, don't bother: I will neither approve nor disapprove. The
> only way for me to know if your changes are correct is to test them,
> and I don't have the time or resources right now to do that. If you
> want to commit them, go ahead. It's your funeral. :)
> 
Understood.  This is some ancient code, and you have lot of modern
stuff to play with.  ;)

Actually, I was just looking for your advise and your vision.

[...]
> And then the stork comes, and it's a driver.
> 
*LOL*


Cheers,
-- 
Ruslan Ermilov
ru at FreeBSD.org
FreeBSD committer
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-net/attachments/20040403/f347d10b/attachment.bin