netdev - Re: Flow Control and Port Mirroring Revisited

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Date:	Tue, 18 Jan 2011 11:41:22 -0800
From:	Rick Jones <rick.jones2@...com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Simon Horman <horms@...ge.net.au>, Jesse Gross <jesse@...ira.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, dev@...nvswitch.org,
	virtualization@...ts.osdl.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: Flow Control and Port Mirroring Revisited

> So it won't be all that simple to implement well, and before we try,
> I'd like to know whether there are applications that are helped
> by it. For example, we could try to measure latency at various
> pps and see whether the backpressure helps. netperf has -b, -w
> flags which might help these measurements.

Those options are enabled when one adds --enable-burst to the pre-compilation 
./configure  of netperf (one doesn't have to recompile netserver).  However, if 
one is also looking at latency statistics via the -j option in the top-of-trunk, 
or simply at the histogram with --enable-histogram on the ./configure and a 
verbosity level of 2 (global -v 2) then one wants the very top of trunk netperf 
from:

http://www.netperf.org/svn/netperf2/trunk

to get the recently added support for accurate (netperf level) RTT measuremnts 
on burst-mode request/response tests.

happy benchmarking,

rick jones

PS - the enhanced latency statistics from -j are only available in the "omni" 
version of the TCP_RR test.  To get that add a --enable-omni to the ./configure 
- and in this case both netperf and netserver have to be recompiled.  For very 
basic output one can peruse the output of:

src/netperf -t omni -- -O /?

and then pick those outputs of interest and put them into an output selection 
file which one then passes to either (test-specific) -o, -O or -k to get CVS, 
"Human" or keyval output respectively.  E.G.

raj@...dy:~/netperf2_trunk$ cat foo
THROUGHPUT,THROUGHPUT_UNITS
RT_LATENCY,MIN_LATENCY,MEAN_LATENCY,MAX_LATENCY
P50_LATENCY,P90_LATENCY,P99_LATENCY,STDDEV_LATENCY

when foo is passed to -o one will get those all on one line of CSV.  To -O one 
gets three lines of more netperf-classic-like "human" readable output, and when 
one passes that to -k one gets a string of keyval output a la:

raj@...dy:~/netperf2_trunk$ src/netperf -t omni -j -v 2 -- -r 1 -d rr -k foo
OMNI TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 
AF_INET : histogram
THROUGHPUT=29454.12
THROUGHPUT_UNITS=Trans/s
RT_LATENCY=33.951
MIN_LATENCY=19
MEAN_LATENCY=32.00
MAX_LATENCY=126
P50_LATENCY=32
P90_LATENCY=38
P99_LATENCY=41
STDDEV_LATENCY=5.46

Histogram of request/response times
UNIT_USEC     :    0:    0:    0:    0:    0:    0:    0:    0:    0:    0
TEN_USEC      :    0: 3553: 45244: 237790: 7859:   86:   10:    3:    0:    0
HUNDRED_USEC  :    0:    2:    0:    0:    0:    0:    0:    0:    0:    0
UNIT_MSEC     :    0:    0:    0:    0:    0:    0:    0:    0:    0:    0
TEN_MSEC      :    0:    0:    0:    0:    0:    0:    0:    0:    0:    0
HUNDRED_MSEC  :    0:    0:    0:    0:    0:    0:    0:    0:    0:    0
UNIT_SEC      :    0:    0:    0:    0:    0:    0:    0:    0:    0:    0
TEN_SEC       :    0:    0:    0:    0:    0:    0:    0:    0:    0:    0
 >100_SECS: 0
HIST_TOTAL:      294547

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