Re: [lwip-users] RE: is this a reentrancy problem with LWIP ver

[David Empson]

"shogun" <address@hidden> wrote:
> Your assumption is correct about the performance it less than I expected.
> Sending a data block 2894 bytes every 200mS is 14.5kBytes/sec and it works
> at that rate.  It appears the fastest I can send that block of data is 
> about
> every 100mS and that is about 28.9k Bytes per second.  If I try to send 
> the
> 2894 byte block every 90mS the send starts failing after 3-4 sends and the
> send returns an out of memory error.  At 90mS, that is only 
> 25.7kBytes/sec.
> These rates should be easy for a 10MBit connection and I am running a
> 100MBit connection.  I know the CPU can affect the performance but I am
> running a 32 bit arm Cortex M# at 80MHz.  Is this typical performance from
> lwip on a TCPIP connection?

I can't comment on expected performance for your platform (I would expect it 
to be higher), but there may be other factors influencing your throughput.

Two major factors will be the window size being offered by the receiver, and 
the amount of buffer space and send queue length in LWIP. If the other 
device starts by offering a small window, then you will only be able to send 
as much data as that window before LWIP will have to stop sending and wait 
for an acknowledgement to arrive. At this point, if you keep supplying 
transmit data to LWIP, it will be filling its buffers while unable to send 
anything. If you haven't configured LWIP to allow sufficient buffered 
transmit data then this will result in out of memory errors.

After a TCP connection is established, it may take a little while for it to 
stabilise with a steady flow of data, so the problem may be as simple as 
increasing the relevant buffers to allow LWIP to hold more data at the start 
of the connection.

The only information you have supplied so far showing the data transmission 
pattern implies your device can send 2894 bytes in three packets within 
approximately 200 microseconds. That's about 14 MB/s but only in a short 
burst.

We may be able to provide more specific help if you could attach a wireshark 
capture which shows the case where you are trying to send data every 90 ms 
and errors are occurring. A copy of your lwipopts.h file might also provide 
some relevant clues.

> On another note, what do I have to be careful of in regards to lwip not
> being reentrant?

If you are using the sockets or netconn API, don't use the same socket or 
netconn from multiple threads. If you are using the raw API, don't allow the 
LWIP core to be invoked from two threads (or from an interrupt handler and 
main code simultaneously).