[uml-user] Re: [uml-devel] Fighting latency

[nils t. <use...@ni...>]

On Fri, Nov 05, 2004 at 12:44:59AM +0100, Blaisorblade wrote:
> On Thursday 04 November 2004 16:50, nils toedtmann wrote:
> > Moin,
> >
> > in some UMLs i run services which do not like latency, eg. VoIP- and
> > gameserver. I previously observed my UMLs going into meditation for a split
> > second every few seconds, but that bucking almost disappeard by taking the
> > usual tuning steps (SKAS, sysemu, $TMP on tmpfs). Nevertheless, my UMLs are
> > still not as responsive as i would like them to. It's not a matter of CPU
> > or network performance. Host and guest are >=95% idle all the time,
> > bandwidth use is far from my UML-bench- marks.
> >
> > I tried to renice the UML processes, but seems not to help (it's hard to
> > measure, just the "feeling" while listening to audio or onlinegaming).
> >
> > Any suggestions?
> >
> > I enabled "PREEMPT" in host kernel. Maybe that's a bad idea?

Any hint for preemtion?


> This problem is an old one. Search the archives for "odd ping problems", which 
> is about long ping delay.

Hmm, it's more like the "network lag" problem. But pings are ok (as long as they
are not too big)

  root@gandalf:~# ping -q -i 0.0005 -s1460 smilla
  PING smilla 1460(1488) bytes of data.

  --- smilla ping statistics ---
  1742 packets transmitted, 1742 received, 0% packet loss, time 22482ms
  rtt min/avg/max/mdev = 1.960/2.831/4.193/0.449 ms, pipe 2, ipg/ewma 12.913/2.760 ms

so i guess my latency-unpleasantness (would not call it problem) it's not a 
netwok problem. I have the old "odd ping problem" (ping payloads >20000), too,
but i do not mind yet ;-)


> A fix was proposed a while ago, which consisted in mlock()ing the memory. But 
> Jeff Dike refused it because he said "I want to write a much more complex and 
> more optimal solution. Mlock() is an hack".
> 
> Even so, I'll try to update the patch, fix it on the security side (that one 
> required setuid()'ing UML, which is purposeless) and push it for inclusion, 
> if possible.

Great, i'll try that.

/nils.


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