svn commit: r277122 - projects/ifnet/sys/dev/msk

[Gleb Smirnoff]

  John,

On Wed, Jan 14, 2015 at 09:33:04AM -0500, John Baldwin wrote:
J> I posted some ideas about how to handle this in a thread several years
J> ago on net@ with various alternatives.  In that case I was focused on
J> buf_ring and I settled on an approach where a draining thread marked the
J> queue as "busy" while it was draining it and cleared that flag before
J> checking the head of the queue.  The enqueue process returned a
J> different errno value (EINPROGRESS or some such) if it queued a packet
J> into a "busy" queue and the transmit routines were changed to 1) always
J> enqueue the packet, and 2) if EINPROGRESS wasn't returned, use a
J> blocking mtx_lock and start transmitting.
J> 
J> However, even this model has some downsides in that one thread might be
J> stuck transmitting packets queued by other threads and never pop back
J> out to userland to service its associated application (a kind of
J> starvation of the user side of the thread).  Note that the mtx_trylock
J> approach has the same problem.  It might be nice to have a sort of limit
J> on the number of packets a thread is willing to enqueue, but then you
J> have the problem of ensuring any packets still on the queue when it hits
J> its limit aren't also delayed indefinitely.

Thanks, I will try to code that.

J> I don't recall the exact mechanics of how Navdeep's mp_ring addresses
J> this (though I believe it does from when I looked at it).
J> 
J> Regardless, I think this was my point I attempted to make on IRC
J> earlier: you need to figure out what you are going to do here first
J> before you go through and convert all the drivers.  Otherwise you will
J> be stuck making multiple passes.  Converting a "real" driver up front is
J> useful so you can prototype different solutions, but I think you need to
J> resolve this now before continuing your pass as the current approach is
J> not suitable to be merged into HEAD.

Right! What I want to do now is to convert several drivers and actually
make project/ifnets usable for people who own several NICs. Then attract
more developers to the problem and using this small set of converted NICs
coin out a final KPI. After that go for a sweep.

-- 
Totus tuus, Glebius.