Herbert Xu [off-list ref] wrote on 01/29/2010 05:03:46 PM:

quoted

Same 5 runs of single netperf's:

0. Driver unsets F_SG but sets F_GSO:
        Org (16K):      BW: 18180.71    SD: 13.485
        New (16K):      BW: 18113.15    SD: 13.551
        Org (64K):      BW: 21980.28    SD: 10.306
        New (64K):      BW: 21386.59    SD: 10.447

1. Driver unsets F_SG, and with GSO off
        Org (16K):      BW: 10894.62    SD: 26.591
        New (16K):      BW: 7262.10     SD: 35.340
        Org (64K):      BW: 12396.41    SD: 23.357
        New (64K):      BW: 7853.02     SD: 32.405


2. Driver unsets F_SG and uses ethtool to set GSO:
        Org (16K):      BW: 18094.11    SD: 13.603
        New (16K):      BW: 17952.38    SD: 13.743
        Org (64K):      BW: 21540.78    SD: 10.771
        New (64K):      BW: 21818.35    SD: 10.598

Hmm, any idea what is causing case 0 to be different from case 2?
In particular, the 64K performance in case 0 appears to be a
regression but in case 2 it's showing up as an improvement.

AFAICS these two cases should produce identical results, or is
this just jitter across tests?

You are right about the jitter. I have run this many times, most
of the times #0 and #2 are almost identical, but sometimes varies
a bit.

Also about my earlier ethtool comment:

Yes, an ethtool bug (version 6). The test case #1 above, I
have written that GSO is off but ethtool "thinks" it is on
(after a modprobe -r cxgb3; modprobe cxgb3). So for test #2,
I simply run "ethtool ... gso on", and GSO is now really on
in the kernel, explaining the better results.

Hmmm, I had a bad ethtool it seems. I built the latest one to
debug this problem but this shows settings correctly.

thanks,

- KK