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xen-devel
[Xen-devel] MPI benchmark performance gap between native linux and domU
Hi all,
I did the following experiments to explore the MPI application execution
performance
on both native linux machines and inside of unpriviledged Xen user domains. I
use 8
machines with identical HW configurations (498.756 MHz dual CPU, 512MB memory,
on a
10MB/sec LAN) and I use Pallas MPI Benchmarks (PMB).
Experiment 1: I boot all 8 nodes with native linux (nosmp, kernel 2.4.29) and
use all
of them for PMB tests.
Experiment 2: I boot all 8 nodes with Xen running and start a single user domain
(port 2.6.10,using file-backed VBD) on each node with 360MB memory. Then I run
the
same PMB tests among these 8 user domains.
The expreiment results show, running a same MPI benchmark in user domains
usually
results in a worse (sometimes very bad) performance comparing with on native
linux machines. The following are the results for PMB SendRecv benchmark for
both
experiments (table1 and table2 report throughput and latency respectively). As
you may
notice, SendRecv can achieve a 14.9MB/sec throughput on native linux machines
but can
get a maximum 7.07 MB/sec throughput if running inside of user domains. The
latency
results also have big gap.
Clearly, there is difference between the memory used in the native linux
machine of
Experiment 1 (512MB) and in the user domain (360MB, can not go higher because
dom0
started with 128MB memory) of Experiment 2. However, I don't think it is the
main
cause of the performance gap because the tested message sizes are much smaller
than
both memory sizes.
I will appreciate your help if you had the similar experience and wanna share
your
insights.
BTW, if you are not familar with PMB SendRecv benchmark, you can find a detailed
explaination at http://people.cs.uchicago.edu/~hai/PMB-MPI1.pdf (see section
4.3.1).
Thanks in advance for you help.
Xuehai
P.S. Table 1: SendRecv throughput (MB/sec) performance
Message_Size(bytes) Experiment_1 Experiment_2
0 0 0
1 0 0
2 0 0
4 0 0
8 0.04 0.01
16 0.16 0.01
32 0.34 0.02
64 0.65 0.04
128 1.17 0.09
256 2.15 0.59
512 3.4 1.23
1K 5.29 2.57
2K 7.68 3.5
4K 10.7 4.96
8K 13.35 7.07
16K 14.9 3.77
32K 9.85 3.68
64K 5.06 3.02
128K 7.91 4.94
256K 7.85 5.25
512K 7.93 6.11
1M 7.85 6.5
2M 8.18 5.44
4M 7.55 4.93
Table 2: SendRecv latency (millisec) performance
Message_Size(bytes) Experiment_1 Experiment_2
0 1979.6 3010.96
1 1724.16 3218.88
2 1669.65 3185.3
4 1637.26 3055.67
8 406.77 2966.17
16 185.76 2777.89
32 181.06 2791.06
64 189.12 2940.82
128 210.51 2716.3
256 227.36 843.94
512 287.28 796.71
1K 368.72 758.19
2K 508.65 1144.24
4K 730.59 1612.66
8K 1170.22 2471.65
16K 2096.86 8300.18
32K 6340.45 17017.99
64K 24640.78 41264.5
128K 31709.09 50608.97
256K 63680.67 94918.13
512K 125531.7 162168.47
1M 251566.94 321451.02
2M 477431.32 707981
4M 997768.35 1503987.61
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