<p>fascinating stuff.</p>
<div class="gmail_quote">On Apr 5, 2013 6:06 PM, "Richard Fuchs" <<a href="mailto:rfuchs@sipwise.com">rfuchs@sipwise.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On 04/05/13 03:53, Daniel-Constantin Mierla wrote:<br>
<br>
> She fallback to user space can happen even during a call? Or is just<br>
> about when the call is initialized, the application detects is some<br>
> problem when setting up forwarding rules in the kernel and goes for user<br>
> space.<br>
<br>
It can happen any time. The socket remains open and the daemon continues<br>
to listen for packets on it. If the daemon receives a packet, it will<br>
process it, which in the normal case will result in it being forwarded.<br>
With the kernel module active and working, the daemon will simply not<br>
see the packets coming in on the socket.<br>
<br>
> Indeed, this is kind of general feeling, at least based on theoretical<br>
> aspects, but I haven't seen any kind of numbers just to compare and see<br>
> how much is worth to go for kernel forwarding.<br>
<br>
I did a very simple test, one pseudo-call (one port in, one port out)<br>
with about 35,000 UDP packets per second going each way. Each packet had<br>
150 bytes payload and the test was done on an 8-core Xeon 2.53 GHz<br>
machine running kernel 2.6.32. Under this workload, the daemon registers<br>
with about 90% single-CPU load without kernel forwarding. The daemon is<br>
multi-threaded and so can use multiple cores, but if it weren't, then it<br>
would be about maxed out at this point. Averaged over the 8 cores this<br>
leaves the system around 88% idle. With kernel forwarding enabled,<br>
system CPU usage drops to >99% idle.<br>
<br>
cheers<br>
<br>
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<br></blockquote></div>