netdev - Re: Flow Control and Port Mirroring Revisited

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Message-ID: <20110123135316.GB2105@verge.net.au>
Date:	Sun, 23 Jan 2011 23:53:16 +1000
From:	Simon Horman <horms@...ge.net.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Rick Jones <rick.jones2@...com>, Jesse Gross <jesse@...ira.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, dev@...nvswitch.org,
	virtualization@...ts.osdl.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: Flow Control and Port Mirroring Revisited

On Sun, Jan 23, 2011 at 12:39:02PM +0200, Michael S. Tsirkin wrote:
> On Sun, Jan 23, 2011 at 05:38:49PM +1100, Simon Horman wrote:
> > On Sat, Jan 22, 2011 at 11:57:42PM +0200, Michael S. Tsirkin wrote:
> > > On Sat, Jan 22, 2011 at 10:11:52AM +1100, Simon Horman wrote:
> > > > On Fri, Jan 21, 2011 at 11:59:30AM +0200, Michael S. Tsirkin wrote:

[snip]

> > > > > Hmm, what is this supposed to measure?  Basically each time you run an
> > > > > un-paced UDP_STREAM you get some random load on the network.
> > > > > You can't tell what it was exactly, only that it was between
> > > > > the send and receive throughput.
> > > > 
> > > > Rick mentioned in another email that I messed up my test parameters a bit,
> > > > so I will re-run the tests, incorporating his suggestions.
> > > > 
> > > > What I was attempting to measure was the effect of an unpaced UDP_STREAM
> > > > on the latency of more moderated traffic. Because I am interested in
> > > > what effect an abusive guest has on other guests and how that my be
> > > > mitigated.
> > > > 
> > > > Could you suggest some tests that you feel are more appropriate?
> > > 
> > > Yes. To refraze my concern in these terms, besides the malicious guest
> > > you have another software in host (netperf) that interferes with
> > > the traffic, and it cooperates with the malicious guest.
> > > Right?
> > 
> > Yes, that is the scenario in this test.
> 
> Yes but I think that you want to put some controlled load on host.
> Let's assume that we impove the speed somehow and now you can push more
> bytes per second without loss.  Result might be a regression in your
> test because you let the guest push "as much as it can" and suddenly it
> can push more data through.  OTOH with packet loss the load on host is
> anywhere in between send and receive throughput: there's no easy way to
> measure it from netperf: the earlier some buffers overrun, the earlier
> the packets get dropped and the less the load on host.
> 
> This is why I say that to get a specific
> load on host you want to limit the sender
> to a specific BW and then either
> - make sure packet loss % is close to 0.
> - make sure packet loss % is close to 100%.

Thanks, and sorry for being a bit slow.  I now see what you have
been getting at with regards to limiting the tests.
I will see about getting some numbers based on your suggestions.

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