Re: Direct Copying To Share Memory In NDIS ProtocolReceive


"Le Chaud Lapin" <jaibuduvin@xxxxxxxxx> wrote in message news:1172849765.066871.323980@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi Thomas & Anton,

On Mar 2, 1:02 am, "Thomas F. Divine" <tdivine@NOpcausaSPAM> wrote:
> -Le Chaud Lapin-

Surely with enough work and debugging you can get your scheme to work. Do
sit back and seriously consider my personal motto: "Keep it simple,
stupid!".

I'm considering, i'm considering. :)

I guess I asked the question in the wrong way. What I should have
done was given context of unchangeable requirements, and ask what is
the best way to do the packet copies.

I have several processes that share a section in RAM, say 27 process,
and one of the processes (prime process) loads a driver that binds to
miniport to send and receive frames. The system is designed so every
frame that is transmitted to the miniports via the protocol must
originate in the shared section, and every frame received from a
miniport via the protocol must be implanted in the shared section. I
currently have 128 frame slots in the shared section, and whenever the
prime process needs to send a frame, it migth not have opportunity to
batch the send, as there might be only 1 frame to send. On receives,
I would like to batch the receives in Protocol receive for bursty
traffic, but bypass copy of queing, copying directly to the shared
section. Since the frame slots are limited, I do not want to try to
guess the optimum preallocation count in ReadFile to batch reads, or I
will starve the other processes of frames.

So I guess my question is, given that the target of all mini-port-
indicated frames must be that shared section, what will be the
performance penalty of copying full packets from the large buffers
setup by ReadFile and the corresponding buffers in the shared
section. Is it much less significant that the kernell transitions.
Also note that this scheme will require a kernel transition anyway,
when ReadFile attempts to lower the semaphore on the frame slots in
the shared section.

-Le Chaud Lapin-

Do make an estimate of the event interactions that must be used to synchronize each "slot". Events that cross the user-kernel boundary will be a performance bottleneck. That's the number that I believe must be minimized to achieve decent performance. (Others may have different thoughts...).

You should still be able to preserve the "safety net" provided by the OS with the inverted call mechanism.

Consider having your "Prime" application allocate user-mode memory that will eventually be shared amongst all your user and kernel components. Pass it to one driver using IRp that is pended, etc. Standard stuff...

I don't see why your "Prime" application couldn't pass the same memory to a second driver also. Having done so, the "Prime" application and two drivers have access to a common memory area. In addition, the system will automatically call both driver's Cleanup/Close routines when the "Prime" application exits. This is the feature that you really don't want to re-invent yourself.

Now the "Prime" application is all set. What about the other processes?

You can share memory across processes using "named shared memory" and "named events", etc. A little work here, but in user-mode only with much less chance of crashes of the system.

Just a thought...

Thomas F. Divine

.

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