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Message-Id: <200706192038.01054.vernux@us.ibm.com>
Date: Tue, 19 Jun 2007 20:38:00 -0700
From: Vernon Mauery <vernux@...ibm.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Jeff Garzik <jeff@...zik.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [-RT] multiple streams have degraded performance
On Monday 18 June 2007 10:12:21 pm Vernon Mauery wrote:
> In looking at the performance characteristics of my network I found that
> 2.6.21.5-rt15 suffers from degraded thoughput with multiple threads. The
> test that I did this with is simply invoking 1, 2, 4, and 8 instances of
> netperf at a time and measuring the total throughput. I have two 4-way
> machines connected with 10GbE cards. I tested several kernels (some older
> and some newer) and found that the only thing in common was that with -RT
> kernels the performance went down with concurrent streams.
I just tested this using lo instead of the 10GbE adapter. I found similar
results. Since this makes it reproducible by just about anybody (maybe the
only factor now is the number of CPUs), I have attached the script that I
test things with.
So with the script run like ./stream_test 127.0.0.1 on 2.6.21 and
2.6.21.5-rt17 I got the following:
2.6.21
=======================
default: 1 streams: Send at 2790.3 Mb/s, Receive at 2790.3 Mb/s
default: 2 streams: Send at 4129.4 Mb/s, Receive at 4128.7 Mb/s
default: 4 streams: Send at 7949.6 Mb/s, Receive at 7735.5 Mb/s
default: 8 streams: Send at 7930.7 Mb/s, Receive at 7910.1 Mb/s
1Msock: 1 streams: Send at 2810.7 Mb/s, Receive at 2810.7 Mb/s
1Msock: 2 streams: Send at 4093.4 Mb/s, Receive at 4092.6 Mb/s
1Msock: 4 streams: Send at 7887.8 Mb/s, Receive at 7880.4 Mb/s
1Msock: 8 streams: Send at 8091.7 Mb/s, Receive at 8082.2 Mb/s
2.6.21.5-rt17
======================
default: 1 streams: Send at 938.2 Mb/s, Receive at 938.2 Mb/s
default: 2 streams: Send at 1476.3 Mb/s, Receive at 1436.9 Mb/s
default: 4 streams: Send at 1489.8 Mb/s, Receive at 1145.0 Mb/s
default: 8 streams: Send at 1099.8 Mb/s, Receive at 1079.1 Mb/s
1Msock: 1 streams: Send at 921.4 Mb/s, Receive at 920.4 Mb/s
1Msock: 2 streams: Send at 1332.2 Mb/s, Receive at 1311.5 Mb/s
1Msock: 4 streams: Send at 1483.0 Mb/s, Receive at 1137.8 Mb/s
1Msock: 8 streams: Send at 1446.2 Mb/s, Receive at 1135.6 Mb/s
--Vernon
> While the test was showing the numbers for receiving as well as sending,
> the receiving numbers are not reliable because that machine was running a
> -RT kernel for these tests.
>
> I was just wondering if anyone had seen this problem before or would have
> any idea on where to start hunting for the solution.
>
> --Vernon
>
> The key for this is 'default' was invoked like:
> netperf -c -C -l 60 -H 10.2.2.4 -t UDP_STREAM -- -m 1472 -M 1472
> and '1Msock' was invoked like:
> netperf -c -C -l 60 -H 10.2.2.4 -t UDP_STREAM -- -m 1472 -M 1472 -s 1M -S
> 1M
>
> 2.6.21
> ==============
> default: 1 streams: Send at 2844.2 Mb/s, Receive at 2840.1 Mb/s
> default: 2 streams: Send at 3927.9 Mb/s, Receive at 3603.9 Mb/s
> default: 4 streams: Send at 4197.4 Mb/s, Receive at 3776.3 Mb/s
> default: 8 streams: Send at 4223.9 Mb/s, Receive at 3848.9 Mb/s
> 1Msock: 1 streams: Send at 4232.3 Mb/s, Receive at 3914.4 Mb/s
> 1Msock: 2 streams: Send at 5428.8 Mb/s, Receive at 3853.2 Mb/s
> 1Msock: 4 streams: Send at 6202.1 Mb/s, Receive at 3774.8 Mb/s
> 1Msock: 8 streams: Send at 6225.1 Mb/s, Receive at 3754.7 Mb/s
>
> 2.6.21.5-rt15
> ===============
> default: 1 streams: Send at 3091.6 Mb/s, Receive at 3048.1 Mb/s
> default: 2 streams: Send at 3768.8 Mb/s, Receive at 3714.2 Mb/s
> default: 4 streams: Send at 1873.6 Mb/s, Receive at 1825.9 Mb/s
> default: 8 streams: Send at 1806.5 Mb/s, Receive at 1792.7 Mb/s
> 1Msock: 1 streams: Send at 3680.4 Mb/s, Receive at 3255.6 Mb/s
> 1Msock: 2 streams: Send at 4129.8 Mb/s, Receive at 3991.5 Mb/s
> 1Msock: 4 streams: Send at 1862.1 Mb/s, Receive at 1787.1 Mb/s
> 1Msock: 8 streams: Send at 1790.2 Mb/s, Receive at 1556.8 Mb/s
View attachment "stream_test" of type "text/plain" (2831 bytes)
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