I have two systems with 82574L NICs. One, name it G (for "generator"), is powerful enough to saturate almost 1G links with small packets (more than 1100Kpps). Other, name it DUT is underpowered and can not process such packet rate. Both G and dut have "set dev.em.0.fc=0". G try to generate traffic to DUT's MAC with netmap & pkt-gen. If G and DUT are connected (no matter how: with direct patchcord or via dedicated switch) G could generate only as much packets as DUT could process! If I remove DUT from dedicated switch, G generates almost-line-rate PPS. If I replace DUT with other system with I210 NIC, G generates same high PPS even if system with I210 can not process it. Looks like 82574L can not turn off flow control. Once again: 82574L -> Switch -> 82574L - pkt-gen generates PPS limited by receiver. 82574L -> 82574L - pkt-gen generates PPS limited by receiver. 82574L -> Switch -> "blackhole" (no other devices attached to switch) - pkt-gen generates line-rate PPS. 82574L -> I210 - pkt-gen generates line-rate PPS. 82574L -> Switch -> I210 - pkt-gen generates line-rate PPS.
Are you using the in-kernel driver in CURRENT on both sides? Do they both have 82574L?
(In reply to Eric Joyner from comment #1) Sorry, I re-read your initial comment; it looks like this problem only occurs when both sides are 82574L. That's interesting.
(In reply to Eric Joyner from comment #2) Both sides are r344277, drivers are compiled in kernel (not loaded as modules). And I didn't tried "i210 -> 82574L" yet, I could try this combination around Monday.
(In reply to Eric Joyner from comment #2) I've added i210 (in form of I210-T1 addon card) to my traffic generator system, and it is limited by receiver (82574L) too! Both ends have FC turned off (with `dev.igb.0.fc=0` and `dev.em.0.fc=0` respective). I've tried with and without switch between. So, two more datapoints: i210 -> Switch -> 82574L - pkt-gen generates PPS limited by receiver. i210 -> 82574L - pkt-gen generates PPS limited by receiver. i210 -> Switch -> "blackhole" (no other devices attached to switch) - pkt-gen generates line-rate PPS.
Inserting manageable switch (HP1800-8G) instead of simple one (HP1400-8G) with explicitly disabled flow control on all ports helps, BTW. But still, i210->i210 doesn't require manageable switch to drop packets on the floor :-)
(In reply to Lev A. Serebryakov from comment #5) Are you able to test with more recent versions? I am interested in this report although I don't have any 82574s that I know of.
(In reply to Kevin Bowling from comment #6) Not now, this old equipment is turned off now and I'm not sure when I'll be able to setup it again...
(In reply to Lev A. Serebryakov from comment #7) I have some systems with 82574L now. Over switched Ethernet I don't see any issues. I will try a direct connect soon. Would help to see sysctl dev.em.0.reg_dump of your machines.
(In reply to Kevin Bowling from comment #8) I'm mboing to new country now and all my "lab" hardware is packed & stored somewhere between in shipping container. I'm not sure, when I will be able to unpack and install it back :-(
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