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    SubjectRe: [1/1] connector/CBUS: new messaging subsystem. Revision number next.
    On 4/26/05, Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:
    > On Tue, 26 Apr 2005 14:06:36 -0500
    > Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
    >
    > > On 4/26/05, Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:
    > > > On Tue, 26 Apr 2005 13:42:10 -0500
    > > > Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
    > > > > Yes, that woudl work, although I would urge you to implement a message
    > > > > queue for callbacks (probably limit it to 1000 messages or so) to
    > > > > allow bursting.
    > > >
    > > > It already exist, btw, but not exactly in that way -
    > > > we have skb queue, which can not be filled from userspace
    > > > if pressure is so strong so work queue can not be scheduled.
    > > > It is of course different and is influenced by other things
    > > > but it handles bursts quite well - it was tested on both
    > > > SMP and UP machines with continuous flows of forks with
    > > > shape addon of new running tasks [both fith fork bomb and not],
    > > > so I think it can be called real bursty test.
    > > >
    > >
    > > Ok, hear me out and tell me where I am wrong:
    > >
    > > By default a socket can receive at least 128 skbs with 258-byte
    > > payload, correct? That means that user of cn_netlink_send, if started
    > > "fresh", 128 average - size connector messages. If sender does not
    > > want to wait for anything (unlike your fork tests that do schedule)
    > > that means that 127 of those 128 messages will be dropped, although
    > > netlink would deliver them in time just fine.
    > >
    > > What am I missing?
    >
    > Concider netlink_broadcast - it delivers skb to the kernel
    > listener directly to the input callback - no queueing actually,

    Right, no queueing for in-kernel...

    But then we have the following: netlink will drop messages sent to
    in-kernel socket ony if it can not copy skb - which is i'd say a very
    rare scenario. Connector, on the other hand, is guaranteed to drop all
    but the very first message sent between 2 schedules. That makes
    connector several orders of magnitude less reliable than bare netlink
    protocol. And you don't see it with your fork tests because you do
    schedule when you fork.

    --
    Dmitry
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