First pass at MSG_FASTOPEN support in top-of-trunk netperf

Folks -

I have just checked-in to the top-of-trunk netperf (http://www.netperf.org/svn/netperf2/trunk) some changes which enable use of sendto(MSG_FASTOPEN) in a TCP_CRR test. While I was checking the system calls I noticed that netperf was calling enable_enobufs() for every migrated test, not just a UDP_STREAM test (the one where it is needed), so I fixed that at the same time. Baseline is taken with the fix in place.

MSG_FASTOPEN is used when one adds a test-specific -F option to the netperf command line:

netperf -t TCP_CRR -H <destination> -- -F

Just testing the client side from a VM on my workstation (running a net-next pulled just before 16:30 Pacific time) to my workstation itself I notice the following:

Without MSG_FASTOPEN:

raj@tardy-ubuntu-1204:~/netperf2_trunk$ src/netperf -H tardy.usa.hp.com -t TCP_CRR -i 3,30
MIGRATED TCP Connect/Request/Response TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to tardy.usa.hp.com () port 0 AF_INET : +/-2.500% @ 99% conf.  : demo
Local /Remote
Socket Size   Request  Resp.   Elapsed  Trans.
Send   Recv   Size     Size    Time     Rate
bytes  Bytes  bytes    bytes   secs.    per sec

16384 87380 1 1 10.00 2092.33
16384 87380

With MSG_FASTOPEN

raj@tardy-ubuntu-1204:~/netperf2_trunk$ src/netperf -H tardy.usa.hp.com -t TCP_CRR -i 3,30 -- -F
MIGRATED TCP Connect/Request/Response TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to tardy.usa.hp.com () port 0 AF_INET : +/-2.500% @ 99% conf.  : demo
!!! WARNING
!!! Desired confidence was not achieved within the specified iterations.
!!! This implies that there was variability in the test environment that
!!! must be investigated before going further.
!!! Confidence intervals: Throughput      : 6.565%
!!!                       Local CPU util  : 0.000%
!!!                       Remote CPU util : 0.000%

Local /Remote

Socket Size   Request  Resp.   Elapsed  Trans.
Send   Recv   Size     Size    Time     Rate
bytes  Bytes  bytes    bytes   secs.    per sec

16384 87380 1 1 10.00 2590.18
16384 87380

There was a ~25% increase in TCP_CRR performance, even without the server actually accepting the magic TCP option. Is that actually expected? Admittedly, it eliminates a connect() call, but the sequence before was:

socket()
getsockopt(SO_SNDBUF)
getsockopt(SO_RCVBUF)
setsockopt(SO_REUSEADDR)
bind()
connect()

sendto(4, "n", 1, 0, NULL, 0)           = 1
recvfrom(4, "n", 1, 0, NULL, NULL)      = 1
recvfrom(4, "", 1, 0, NULL, NULL)       = 0

close(4)

and with MSG_FASTOPEN only the connect() goes away. Unless connect() is really heavy compared to what sendto(MSG_FASTOPEN) does or something else has changed wrt behaviour.

Anyway, feel free to kick the tires on the netperf changes and let me know of any problems you encounter.

happy benchmarking,

rick jones

Hi Rick,

I have a locally enhanced netperf for TCP_CRR over Fast Open and I've
noticed the numbers can change drastically between runs. I have not got
the time to investigate why. (Does it have to do with scheduler and CPU locality?) How consistent is your perf number?

I plan to submit the server side code soon and will work with you to add the server side support to TCP_CRR (it requires a new TCP_FASTOPEN socket option to enable Fast Open on a listener.)

Thanks,

Jerry

I recall the performance being reasonably consistent but there has been a vacation of my own in the middle there so my dimm memory is a bit fuzzy :)

Historically (and going beyond just Linux) a TCP_CRR test can have some non-trivial run to run variation thanks to (attempted) TIME_WAIT reuse.
Whether that is happening to you I don't know, but it might be worth a
look.

Works for me.

happy benchmarking,

rick jones