Hello, I recycled an older box and put an i350-2 together with a second 82541GI (PCI-slot, one already on-board) into it. The two i350-ports are used with VMDq for ESXi5.1. The two 82541GI are used as lagg-nics by a 9.2-RC (amd64) guest as passthrou PCI device. Always had good results with such setups, but found out, that nics which use the legacy driver part of if_em max out at ~0.6Gbits/s (1500 MTU).
There's another NIC on board of this recycle-box, a 82566-PHY (ICH9 integrated MAC). This one uses also if_em, but not legacy code, it reports version 7.3.8 (compared to 1.0.6). And it has no problem fully saturating GbE (~925Mbits/s, no jumbo Frames support anyways). I'm using iperf, with and without lagg (doesn't change anyhing, like it doesn't influence tests on some other boxes with 82576 and i350 (igb)) I see enough idle cycles so CPU shouldn't limit the legacy if_em nics. Also, I see the 82541 consuming arround 8k irqs. Same does the 82566-PHY, but with much higher throughput... I'd like to know if I can't generally expect to saturate older (PCI) GbE nics the line for any reason... I can remember tigeon cards from more than a decade ago, which indeed seemd to lack the performance to gain GbE, but I thought that was no issue shortly later and no "modern" Intel-GbE card had such constraints!? Is there any special tuning for legacy if_em (no need for any TCP tuning, 82566 doesn't have any issue)? Thanks, -Harry
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