Issue with rate-limiting engine

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Have a set up where I'm using OpenPGM on the server-side, MS-PGM on the 
client-side trying to multicast a large file.  What I'm running into is an odd 
performance problem when trying to increase the speed.

For example (on the sender):
PGM_MTU: 7500
PGM_TXW_MAX_RTE: 7,000,000

Operates as I would expect, with an approx. speed of ~7000KB/sec

However, when I change PGM_TXW_MAX_RTE to 8,000,000, the rate drops to the 
floor.  It's not the repair cycle or anything, it's the rate of packets coming 
from the sender.  If I increase the PGM_MTU value to 9000, then performance 
picks back up.

Looking at the code, I think the problem is in the calculations done during 
setup in the rate engine.  Specifically, looking at pgm_rate_create in 
rate_control.c, I see:

    if ((rate_per_sec / 1000) >= max_tpdu) {
        bucket->rate_per_msec   = bucket->rate_per_sec / 1000;
        bucket->rate_limit  = bucket->rate_per_msec;
    } else {
        bucket->rate_limit  = bucket->rate_per_sec;
    }

My first impression is that bucket->rate_limit is being set wrong, shouldn't 
that be bucket->rate_limit = bucket->rate_per_sec?

The basic work flow for the sending loop (non-blocking) is to send, check the 
status code, and in the case of PGM_IO_STATUS_RATE_LIMITED, use pgm_getsockopt 
to fetch PGM_RATE_REMAIN.  Once PGM_TXW_MAX_RTE/1000 is >= PGM_MTU, the values 
returned skyrocket, causing the sender to slow down greatly.

So I'm trying to figure out if this is a.) a mistake on our part with the 
program flow, or b.) a bug in OpenPGM.

Additional bit:
- server is running on FreeBSD 7.0
- we're using libpgm-5.2.122
- client is running on Windows 7 using MS-PGM

Thanks,

Jon

Original issue reported on code.google.com by [email protected] on 22 May 2013 at 6:31