Re: Regression: Approximate 34% performance hit in receive throughput over ixgbe seen due to build_skb patch

On May 22, 2018, at 12:23 PM, Alexander Duyck [off-list ref] wrote:

3. There should be a private flag that can be updated via "ethtool
--set-priv-flags" called "legacy-rx" that you can enable that will
roll back to the original that did the copy-break type approach for
small packets and the headers of the frame.

With legacy-rx enabled, most of the regression goes away, but it's still present
as compared to the code without the patch; the regression then drops to about 6%:

# ethtool --show-priv-flags eno1
Private flags for eno1:
legacy-rx: on

Socket  Message  Elapsed      Messages                
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

 65536      64   60.00     35934709      0     306.64
 65536           60.00     33791739            288.35

Socket  Message  Elapsed      Messages                
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

 65536      64   60.00     39254351      0     334.97
 65536           60.00     36761069            313.69

Is this variance to be expected, or do you think modification of the
interrupt delay would achieve better results?


    William Kucharski