David Laight [off-list ref] wrote on 21/08/2014 05:29:41 PM:

From: David Laight <redacted>
To: Razya Ladelsky/Haifa/IBM@IBMIL, "Michael S. Tsirkin" 

[off-list ref]

Cc: "abel.gordon@gmail.com" <redacted>, Alex Glikson/
Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Joel Nider/Haifa/
IBM@IBMIL, "kvm@vger.kernel.org" [off-list ref], "linux-
kernel@vger.kernel.org" [off-list ref], 
"netdev@vger.kernel.org" [off-list ref], 
"virtualization@lists.linux-foundation.org" 
[off-list ref], Yossi 

Kuperman1/Haifa/IBM@IBMIL

Date: 21/08/2014 05:31 PM
Subject: RE: [PATCH] vhost: Add polling mode

From: Razya Ladelsky

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"Michael S. Tsirkin" [off-list ref] wrote on 20/08/2014 01:57:10 PM:

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Results:

Netperf, 1 vm:
The polling patch improved throughput by ~33% (1516 MB/sec -> 

2046 MB/sec).

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Number of exits/sec decreased 6x.
The same improvement was shown when I tested with 3 vms running 

netperf

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(4086 MB/sec -> 5545 MB/sec).

filebench, 1 vm:
ops/sec improved by 13% with the polling patch. Number of exits
was reduced by 31%.
The same experiment with 3 vms running filebench showed similar 

numbers.

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Signed-off-by: Razya Ladelsky <redacted>

This really needs more thourough benchmarking report, including
system data.  One good example for a related patch:
http://lwn.net/Articles/551179/
though for virtualization, we need data about host as well, and if 

you

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want to look at streaming benchmarks, you need to test different 

message

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sizes and measure packet size.

Hi Michael,
I have already tried running netperf with several message sizes:
64,128,256,512,600,800...
But the results are inconsistent even in the baseline/unpatched
configuration.
For smaller msg sizes, I get consistent numbers. However, at some 

point,

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when I increase the msg size
I get unstable results. For example, for a 512B msg, I get two 

scenarios:

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vm utilization 100%, vhost utilization 75%, throughput ~6300
vm utilization 80%, vhost utilization 13%, throughput ~9400 (line 

rate)

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I don't know why vhost is behaving that way for certain message sizes.
Do you have any insight to why this is happening?

Have you tried looking at the actual ethernet packet sizes.
It may well jump between using small packets (the size of the writes)
and full sized ones.

I will check it,
Thanks,
Razya

If you are trying to measure ethernet packet 'cost' you need to use UDP.
However that probably uses different code paths.

   David