[dpdk-dev] Receive queue full

["François-Frédéric Ozog" <ff@ozog.com>]

Hi,

I am bumping into a similar problem than the one explained here
(https://www.mail-archive.com/e1000-devel@lists.sourceforge.net/msg07684.htm
l): At some point in time, a receive queue gets "FULL" i.e. tail==head
(reading the NIC registers) and the thread associated to that queue cannot
retrieve any packet from it.

The test program derived from L2FWD echoes packets received on one port back
to the same port, it reads up to 32 packets and send them back. The echo
works nicely for a few seconds then queues gets full and stall.

I have found that setting rx_conf.rx_free_thresh down from 32 to 28 (the
multiple of 4 just before 32) avoids the problem and can handle close to
10Mpps per port. 

Test context:
	- 4 socket Xeon E7 4800v2 with 256GB RAM
	- 32GB hugepages reserved, 104 lcores reserved
	- DPDK 1.5.0, testing with the latest from git presents a
performance glitch I can't pinpoint at present.
	- two ports (either 82599ES or X540) loaded at 10Mpps
	- various tests with 2 to 15 receive queues per port
	- various tests with different combinations of RX_PTHRESH,
RX_HTHRESH, RX_WTHRESH

It really looks like a race condition (32 reads, 32 refresh cycle) but I
can't figure it out if it exists.

I'd be glad to get any comment or question on the issue.

Cordially,

François-Frédéric