Re: CVS commit: src/sys/net

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

On Wed, Feb 17, 2016 at 4:52 PM, Taylor R Campbell
<campbell+netbsd-source-changes-d%mumble.net@localhost> wrote:
>    Date: Wed, 17 Feb 2016 15:12:31 +0900
>    From: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
>
>    On Wed, Feb 17, 2016 at 2:13 PM, Taylor R Campbell
>    <campbell+netbsd-source-changes-d%mumble.net@localhost> wrote:
>    > Note that this queueing takes effect only if the link state changes
>    > multiple times within maybe a few microseconds, before the softint can
>    > run.  If your link state is changing that many times so quickly,
>    > losing an event or two is probably the least of your worries
>
>    Yeah, it's nitpicking, but for that reason, I think it's better to pass
>    events as they are to userland.
>
>    > -- but
>    > you're probably more interested in seeing something like ...down...up
>    > than ...up/up/up.
>
>    Yes. (up/up/up events are eliminated in the first place though.)
>
> So what events would you choose to skip, if not the scheme that Roy
> described?

(I think I confused you, sorry...)

I rather want to not skip anything as much as possible
(except for repeating same events (e.g., up/up/up) because
keeping them all changes the original behavior).

I intend to skip/eliminate events only if there are too many
events happen in a short period (i.e., need queuing) to protect
the system from overloading. In that case (it's a very rare case
I think), we just drop an earliest event first.

>
> I bet that, whatever events you would choose to skip, we can still
> prove that the resulting queues need be no longer than, say, three
> elements, and we'd still usefully report link flapping to userland --
> as long as we can make enough progress to run softints and userland
> processes at all.
>
> Here are some example reductions that intuitively sound reasonable to
> me:
>
> down/down = down
> up/up = up
> down/unknown/up = down/up
> down/up/down = down
>
> What other sequences of events would you simplify?

As I said, I want to keep the sequences (except for repeating same events)
so the last two examples will be sent as they are.

  ozaki-r