Yes it's hard to trust virtualized stuff because you have no idea what they skimp on in terms of realtime access.<br><br>I won't endorse using FS on a VM as i have not done it very extensively beyond openvz but I can<br>
point out a few reasons why it has a fighting chance.<br><br>FS uses a timer architecture designed to amplify the work of one timer thread into every timer open<br>by FS. This single thread uses the monotonic clock on the system to try and perfrom a 1ms accurate loop.<br>
<br>This single loop updates a soft value for current epoch time and microsecond epoch time with the goal<br>of (again) being as close as possible to being accurate to 1 ms. <br><br>The timer loop also has a global matrix to all of the timing intervals being subscribed to by a timer open by FS.<br>
The loop will tick a counter in each unique timing interval (10ms, 20ms, 60ms etc) and fire a conditional broadcast to all of the timers who are blocking for a tick. This is not perfectly accurate but close enough to end up plus or minus 2ms in resulting rtp traces. <br>
<br>So as long as the VM will expose the syscall down to the real monotonic clock rather than doing it's own soft timing technique you have a better chance for success.<br><br>The other issue with VM is with vmware, the bridged networking mode seems to send 2 of every RTP<br>
packet to the channel resulting in garbled audio from the obvious timing issue introduced from too many packets.<br><br>Anyway evaluating FS with a VM is a good way to get acquainted but, with all the money saved choosing FS, many can afford to buy it a nice 8 core box for it to live on and still have money left over to support the project or ClueCon 2009 this august ;)<br>
<br><br><div class="gmail_quote">On Fri, Jan 16, 2009 at 2:17 AM, Kristian Kielhofner <span dir="ltr"><<a href="mailto:kristian.kielhofner@gmail.com">kristian.kielhofner@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Speaking of networking...<br>
<br>
After timing that's the next "achilles heel" of RTP handing with virtualization.<br>
<br>
Very, very few of these platforms were designed to handle massive<br>
numbers of very small RTP packets. Everything from interrupt handling<br>
on the actual ethernet adapter to getting the data into userspace<br>
within the virtual instance is worrisome:<br>
<br>
<a href="http://www.xen.org/files/xensummit_4/NetworkIO_Santos.pdf" target="_blank">http://www.xen.org/files/xensummit_4/NetworkIO_Santos.pdf</a><br>
<a href="http://forum.openvz.org/index.php?t=msg&goto=11619&" target="_blank">http://forum.openvz.org/index.php?t=msg&goto=11619&</a><br>
<br>
Interestingly enough the Xen paper makes it out to be really bad yet<br>
the OpenVZ post praises Xen's performance. Without any real testing,<br>
who knows? I just know that scaling 50pps per RTP stream (20ms<br>
packetization) can be difficult enough on native hardware, let alone<br>
[virtualization technology du jour].<br>
<br>
On Thu, Jan 15, 2009 at 5:02 PM, Remko Kloosterman<br>
<div class="Ih2E3d"><<a href="mailto:R.Kloosterman@mtel.nl">R.Kloosterman@mtel.nl</a>> wrote:<br>
</div><div><div></div><div class="Wj3C7c">> Lot's of experience and suggestions here. Thanks.<br>
><br>
> I believe it should be theoretically possible to have blip-free RTP<br>
> streaming through the appliance. Most windows ethernet drivers allow for<br>
> QoS packet scheduling. If the VMware network bridge driver honors this<br>
> and syncs the buffers at 20ms frames (or whatever frame size applies)<br>
> you should be able to schale up a bit and maintain low jitter.<br>
><br>
> Anyone knows how the VMware network bridge exactly works?<br>
><br>
><br>
> -----Oorspronkelijk bericht-----<br>
> Van: <a href="mailto:freeswitch-users-bounces@lists.freeswitch.org">freeswitch-users-bounces@lists.freeswitch.org</a><br>
> [mailto:<a href="mailto:freeswitch-users-bounces@lists.freeswitch.org">freeswitch-users-bounces@lists.freeswitch.org</a>] Namens Gregory<br>
> Boehnlein<br>
> Verzonden: donderdag 15 januari 2009 21:37<br>
> Aan: <a href="mailto:freeswitch-users@lists.freeswitch.org">freeswitch-users@lists.freeswitch.org</a><br>
> Onderwerp: Re: [Freeswitch-users] [Freeswitch-dev] VMWare voice quality<br>
><br>
>> To the contrary, we have had quite good results in virtualized<br>
>> environments and you don't really need timing that is that accurate to<br>
><br>
>> make it work.<br>
><br>
> If you don't handle RTP, I'm sure it is amazing. However, if you have to<br>
> do voicemail, stream audio from the server or do any kind of actual<br>
> time/latency/jitter sensitive processing, I don't care how much you tune<br>
> your hypervisor, it's never going to scale.<br>
><br>
>> We work quite well on amazon EC2 for example. There are 2 issues I<br>
>> know about with vmware, 1 is you need to set a setting on the host to<br>
>> extend somewhat sane clocks being available, the second is I have seen<br>
><br>
>> issues with the bridged network adapter actually doubling up all<br>
>> packets causing very strange issues, I suggest not using bridged<br>
>> networking if you experience this.<br>
><br>
> I've not seen this behavior on Vmware ESX 3.5u2. Maybe an issue on<br>
> Vmware Server or Workstation?<br>
><br>
><br>
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<br>
<br>
</div></div><font color="#888888">--<br>
Kristian Kielhofner<br>
<a href="http://blog.krisk.org" target="_blank">http://blog.krisk.org</a><br>
<a href="http://www.submityoursip.com" target="_blank">http://www.submityoursip.com</a><br>
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</font><div><div></div><div class="Wj3C7c"><br>
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