(Please keep me CC'd to all comments/responses)
I've tried a kernel upgrade from 3.4.2 to 4.4.0 and see a marked drop in
networking performance. Nothing was changed on the test systems, other than
the kernel itself (and kernel modules). The identical .config used to build
the 3.4.2 kernel was brought over into the 4.4.0 kernel source tree, and any
configuration differences (e.g. new parameters, etc.) were taken as default
values.
The testing was performed on the same actual hardware for both kernel versions
(i.e. take the existing 3.4.2 physical setup, simply boot into the (new) kernel
and run the same test). The netperf utility was used for benchmarking and the
testing was always performed on idle systems.
TCP testing yielded the following results, where the 4.4.0 kernel only got
about 1/2 of the throughput:
Recv Send Send Utilization
Service Demand
Socket Socket Message Elapsed Send Recv Send
Recv
Size Size Size Time Throughput local remote local
remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB
us/KB
3.4.2 13631488 13631488 8952 30.01 9370.29 10.14 6.50 0.709
0.454
4.4.0 13631488 13631488 8952 30.02 5314.03 9.14 14.31 1.127
1.765
SCTP testing yielded the following results, where the 4.4.0 kernel only got
about 1/3 of the throughput:
Recv Send Send Utilization
Service Demand
Socket Socket Message Elapsed Send Recv Send
Recv
Size Size Size Time Throughput local remote local
remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB
us/KB
3.4.2 13631488 13631488 8952 30.00 2306.22 13.87 13.19 3.941
3.747
4.4.0 13631488 13631488 8952 30.01 882.74 16.86 19.14
12.516 14.210
The same tests were performed a multitude of time, and are always consistent
(within a few percent). I've also tried playing with various run-time kernel
parameters (/proc/sys/kernel/net/...) on the 4.4.0 kernel to alleviate the
issue but have had no success at all.
I'm at a loss as to what could possibly account for such a discrepancy...
