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    SubjectRe: [PATCH] support for Cobalt Networks (x86 only) systems (forrealthis

    On Fri, 1 Jun 2001, Bogdan Costescu wrote:

    > On Fri, 1 Jun 2001, jamal wrote:
    > > One idea i have been toying with is to maintain hysteris or threshold of
    > > some form in dev_watchdog;
    > AFAIK, dev_watchdog is right now used only for Tx (if I'm wrong, please
    > correct me!). So how do you sense link loss if you expect only high Rx
    > traffic ?

    Good question. Makes me think. Thoughts further below.

    > > example: if watchdog timer expires threshold times, you declare the link
    > > dead and send netif_carrier_off netlink message.
    > > On recovery, you send netif_carrier_on
    > I assume that you mean "on recovery" as in "first succesful hard_start_xmit".


    > > Assumption:
    > > If the tx path is blocked, more than likely the link is down.
    > Yes, but is this a good approximation ? I'm not saying that it's not, I'm
    > merely asking for counter-arguments.

    It is an indirect approximation. Note that if the system data is very
    asymetrical as in the case you pointed out, notification will take a long
    long time. You need a plan B. Still, the tx watchdogs are a good source of
    fault detection in the case of non-availabilty of MII detection and even
    with the presence of MII.

    I hate making this more complex than it should be:

    Since we already have a messaging system within the kernel and
    user<->kernel space aka "netlink" -- one could easily add a protocol in
    user space which "dynamically heartbeats" the devices. Control should come
    from user space; it would be a great idea to avoid ioctls.

    "Dynamic" in the above sense means trying to totaly avoid making it a
    synchronous poll. The poll rate is a function of how many packets go out
    that device per average measurement time. Basically, the period that the
    user space app dumps "hello" netlink packets to the kernel is a variable.


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