On Tuesday 28 March 2006 01:42, David Lang wrote:
> yOn Mon, 27 Mar 2006, David Lang wrote:
> > I foolishly attempted to startup 25 uml instances on one system (dual 252
> > opterons with 8G of ram, each um instance getting 256M)
> > what I found was that they seem to be getting in each others way a LOT
> > (just on system boot), vmstat on the host is showing almost all of the
> > cpu time (80%+) being spent in the system, not in userspace (which
> > surprised me)
> > so before I spend much time gathering info to try and debug this I wanted
> > to ask what the current limits are, and if the limits should just be cpu
> > and ram, then I'll do more digging to find out what's happening in my
> > case.
> well, I reduced the count to 19 instances, and upped the ram on each one
> to 400M (they were hitting oom with only 256m each)
> almost an hour later the machines still haven't finished booting with top
> looking basicly the same for the last half hour or so.
> top - 16:42:18 up 4 days, 23:11, 25 users, load average: 16.79, 16.65,
> 16.23 Tasks: 44193 total, 14 running, 139 sleeping, 44040 stopped, 0
> zombie Cpu0 : 2.3% us, 97.7% sy, 0.0% ni, 0.0% id, 0.0% wa, 0.0% hi,
> 0.0% si Cpu1 : 3.2% us, 96.7% sy, 0.0% ni, 0.0% id, 0.0% wa, 0.0% hi,
> 0.1% si Mem: 8186088k total, 8145620k used, 40468k free, 11436k
> buffers Swap: 2048276k total, 0k used, 2048276k free, 4959636k
> cached
> so far it looks to me like ram is Ok, but the high system percentage looks
> strange to me. the system closest to finishing it's boot has used a little
> over 10 min of cpu time (>5x the normal wall clock time for the boot) so
> I am running into contention at some point here.
I know that it's maybe a bad workaround, but what about sequential startup
both of UMLs and of the jobs inside them?
I'd run "vmstat 1" to watch for increase of context switches - an eccessive
amount of them is likely to burn you out.
Look below (I'm selecting the context switches count with awk) - the low
numbers (~1000-2000) are with the system running only a CPU-hog in
background, the high ones (~100 000) are when I run inside UML:
$ while :; do /bin/true; done
vmstat 1|awk '{print $12}'
cs
2714
113208
92306
109654
82226
1478
1235
84262
114143
115037
112424
But with apache benchmark on a UML, I can get higher numbers:
$ ab2 -t 30 -v 1 Sarge/apache2-default/
cs
5170
945
1089
977
756
1083
24879
106316
119013
121471
99706
122907
127361
108613
130089
126837
123382
116747
130797
131173
129478
cs
124357
124892
102280
127380
129434
109804
113807
123767
133519
125085
119384
129109
129997
126418
60348
892
675
743
851
655
780
--
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
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