linux-kernel - Re: [PATCH] vhost: Add polling mode

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Date:	Thu, 21 Aug 2014 17:23:55 +0300
From:	Razya Ladelsky <RAZYA@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	abel.gordon@...il.com, Alex Glikson <GLIKSON@...ibm.com>,
	Eran Raichstein <ERANRA@...ibm.com>,
	Joel Nider <JOELN@...ibm.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Yossi Kuperman1 <YOSSIKU@...ibm.com>
Subject: Re: [PATCH] vhost: Add polling mode

"Michael S. Tsirkin" <mst@...hat.com> wrote on 20/08/2014 01:57:10 PM:

> > Results:
> > 
> > Netperf, 1 vm:
> > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 
MB/sec).
> > Number of exits/sec decreased 6x.
> > The same improvement was shown when I tested with 3 vms running 
netperf
> > (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.
> > 
> > Signed-off-by: Razya Ladelsky <razya@...ibm.com>
> 
> 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
> want to look at streaming benchmarks, you need to test different message
> 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, 
when I increase the msg size
I get unstable results. For example, for a 512B msg, I get two scenarios:
vm utilization 100%, vhost utilization 75%, throughput ~6300 
vm utilization 80%, vhost utilization 13%, throughput ~9400 (line rate)

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

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