Messages in this thread | | | Date | Tue, 26 Apr 2005 15:02:01 -0500 | From | Dmitry Torokhov <> | Subject | Re: [1/1] connector/CBUS: new messaging subsystem. Revision number next. |
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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.
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