Please do not top post on netdev. On Wed, 2017-11-08 at 11:04 -0500, Vitaly Davidovich wrote: > So this issue is somehow related to setting SO_RCVBUF *after* > connecting the socket (from the client). The system is configured > such that the default rcvbuf size is 1MB, but the code was shrinking > this down to 75Kb right after connect().
What are you calling default rcvbuf size exactly ? Is the application doing s = socket(...); ... setsockopt(s, SOL_SOCKET, SO_RCVBUF, [1000000], 4) ... connect(s, ...) setsockopt(s, SOL_SOCKET, SO_RCVBUF, [75000], 4) > I think that explains why > the window size advertised by the client was much larger than > expected. I see that the kernel does not want to shrink the > previously advertised window without advancement in the sequence > space. So my guess is that the client runs out of buffer and starts > dropping packets. Not sure how to further debug this from userspace > (systemtap? bpf?) - any tips on that front would be appreciated. You could provide a packet capture (tcpdump) for a start ;)
