Date: Sat, 30 Jun 2001 11:24:06 -0500 From: David Leimbach <dleimbac@earthlink.net> To: questions@freebsd.org Subject: Real numbers on why loopback is slow in FreeBSD please read... Message-ID: <20010630112406.A1143@mutt.home.net>
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It seems that the recent flood of stupid micro-optimization questions
[Some of which were mine involving gettimeofday] has made people on this
list ignore questions where anyone says anything along the lines of...
"FreeBSD has a really slow .... compared to ...."
Many of these questions may actually be dumb or trolls or flaimbait but
other people have valid questions.
I asked one yesterday where I wanted to know how I can speed up the
performance of the loopback device. The reason I asked was that I would
like to be able to run MPI jobs on FreeBSD someday and I am involved in
porting one implementation of MPI to FreeBSD.
I noticed the really horribly poor latency of FreeBSD when using the loopback.
Here are some numbers:
[From the perf MPI test on FreeBSD ]
Msg_len Latency Rate Strm Latency Strm Rate
[byte] [us] [MB/s] [us] [MB/s]
0 223.44 0.00 173.35 0.00
4 331.89 0.01 183.77 0.02
8 331.54 0.02 175.11 0.04
16 331.72 0.05 174.81 0.09
32 331.64 0.09 181.86 0.17
64 332.71 0.18 348.80 0.17
128 333.13 0.37 216.24 0.56
256 344.48 0.71 425.06 0.57
512 348.74 1.40 422.60 1.16
1024 361.96 2.70 229.65 4.25
2048 368.53 5.30 209.90 9.31
4096 411.84 9.48 485.78 8.04
8192 492.99 15.85 573.21 13.63
[Same test in Linux different machine 2.4.0 kernel]
Msg_len Latency Rate Strm Latency Strm Rate
[byte] [us] [MB/s] [us] [MB/s]
0 40.11 0.00 204.50 0.00
4 49.60 0.08 174.45 0.02
8 49.21 0.16 216.60 0.04
16 49.35 0.31 181.85 0.08
32 49.35 0.62 218.98 0.14
64 49.22 1.24 181.95 0.34
128 49.67 2.46 218.81 0.56
256 49.73 4.91 202.71 1.20
512 54.22 9.01 33.34 14.65
1024 52.49 18.61 34.92 27.97
2048 53.07 36.80 59.23 32.97
4096 67.57 57.81 69.64 56.09
8192 82.55 94.64 146.57 53.30
So I think I have valid reason to be worried. This is just a ping-pong
test that perf runs but the message latency on linux is more desirable
than FreeBSD.
Is this related to proc speeds at all? If so how much?
I would like to do better than 223.44 ms latency for a 0 data length packet
in FreeBSD.
Any ideas??
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