Re: [PATCH] TX algorithms, missetting IFF_OACTIVE and if_timer

From: Ruslan Ermilov (ru_at_FreeBSD.ORG)
Date: 04/03/04

  • Next message: Eugene Grosbein: "Re: MRTG no SNMP" 
    Date: Sat, 3 Apr 2004 02:49:52 +0300
To: Bill Paul <wpaul@FreeBSD.ORG>

    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@FreeBSD.org
FreeBSD committer

  • Next message: Eugene Grosbein: "Re: MRTG no SNMP"

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