read() returns ETIMEDOUT on steady TCP connection

[Tim Gebbett]

Hi Andre, did some careful testing yesterday and last night. I seem to 
be still hitting an unknown buffer although the probem is  much alleviated.
The system achieved a 7hour run at 500mbit where ETIMEDOUT occured. I 
was feeding 11 other streams to the server whos counters show an 
uninterrupted eleven hours. The feeder streams are from the same source, 
so it is unlikely that the one feeding the test could of had a problem 
without affecting the counters of the others.
sysctls are:

(loader.conf) hw.em.txd=4096
net.inet.tcp.sendspace=78840
net.inet.tcp.recvspace=78840

kern.ipc.nmbjumbop=51200
kern.ipc.nmbclusters=78840
kern.maxfiles=50000

IP stats are miraculously improved, going from a 10% packet loss within 
stack (output drops) to a consistent zero at peaks of 80000 pps. I 
believe the problem is now being shunted  to the NIC from the following 
output:

dev.em.0.debug=1

< em0: Adapter hardware address = 0xc520b224

< em0: CTRL = 0x48f00249 RCTL = 0x8002 
< em0: Packet buffer = Tx=16k Rx=48k 
< em0: Flow control watermarks high = 47104 low = 45604
< em0: tx_int_delay = 66, tx_abs_int_delay = 66
< em0: rx_int_delay = 0, rx_abs_int_delay = 66
< em0: fifo workaround = 0, fifo_reset_count = 0
< em0: hw tdh = 3285, hw tdt = 3285
< em0: hw rdh = 201, hw rdt = 200
< em0: Num Tx descriptors avail = 4096
< em0: Tx Descriptors not avail1 = 4591225
< em0: Tx Descriptors not avail2 = 0
< em0: Std mbuf failed = 0
< em0: Std mbuf cluster failed = 0
< em0: Driver dropped packets = 0
< em0: Driver tx dma failure in encap = 0

dev.em.0.stats=1

< em0: Excessive collisions = 0

< em0: Sequence errors = 0
< em0: Defer count = 0
< em0: Missed Packets = 16581181
< em0: Receive No Buffers = 74605555
< em0: Receive Length Errors = 0
< em0: Receive errors = 0
< em0: Crc errors = 0
< em0: Alignment errors = 0
< em0: Collision/Carrier extension errors = 0
< em0: RX overruns = 289717
< em0: watchdog timeouts = 0
< em0: XON Rcvd = 0
< em0: XON Xmtd = 0
< em0: XOFF Rcvd = 0
< em0: XOFF Xmtd = 0
< em0: Good Packets Rcvd = 848158221
< em0: Good Packets Xmtd = 1080368640
< em0: TSO Contexts Xmtd = 0
< em0: TSO Contexts Failed = 0


Does the counter 'Tx Descriptors not avail1'  indicate lack of  
decriptors at the time not available, and would this be symptomatic of  
something Mark suggested:
"(the stack) needs to handle local buffer fills not as a failed attempt 
on transmission that increments the retry counter, a possible better 
strategy required for backoff
when the hardware buffer is full?"

Thanks for your continued time and effort - Tim


Andre Oppermann wrote:
> Tim Gebbett wrote:
>> Hi all,
>>
>> applied the patch,
>>
>> Well before a ETIMEDOUT error occurred (around 60secs), the tcp debug 
>> started venting massive
>> quantities of tcp_output error 55 while sending with syncache noise:
>
> The error seems to be coming from the interface send queue which hits 
> the limit.
> If you are using em(4) network interface please add this line to 
> loader.conf(5):
>
>  hw.em.txd=1024
>
> Or even more if problems persist.  The maximum is 4096.
>