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

Hi Rick,

On Mon, Aug 6, 2012 at 6:47 PM, Rick Jones [off-list ref] wrote:

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?

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

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
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