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* question regarding strange kernel stats under high (network) load
@ 2004-05-23 15:33 Willem de Bruijn
0 siblings, 0 replies; only message in thread
From: Willem de Bruijn @ 2004-05-23 15:33 UTC (permalink / raw)
for a network monitoring project that I'm working on (see my sig if you're
interested) I have to compare system load under high throughput. Directly
comparing my implementation to tcpdump (LSF) seems fine, our user% and
kernel% are lower. However, when I added an idle system I noticed some
strange behaviour that remains on re-executing the tests:
the kernel% is actually higher when nothing is running than when my code is
running! Overall processing is lower (idle% is higher on the idle system),
but that is thanks to the high %si (soft ints) that my code generates.
In order to better explain my problem here is the output of top (the new one,
with %si, %hi and %wa) for a 600Mbit throughput, the first line is for the
idle system, the second for FFPF (my system) and the third for Linux Socket
Mbit iperf in iperf out capt recv kern drop % drop tcpdump % iperf % user %
kernel % idle %
600 608 608 33 6 30 40
600 608 608 514084 517314 33 0.63 17 20 13 15 25
600 609 608 421215 517597 96382 31.4 76 33 17 49.5 0
the usage statistics are user%, kernel% and idle% (I haven't saved the si%
results). What's odd is that although idle is higher for the idle system,
kernel% is actually lower. I can understand that my code generates extra soft
interrupts, but not that it has an effect on the `other' kernel load. Perhaps
I don't understand the values good enough, in which case I would greatly
appreciate your help. However, it could also signal a bug in the statistics
reporting (although I don't hope that's the case, these results are great for
my paper :). FYI, I used the command
top -b -n 5 -d 3 | grep "Cpu\|tcpdump\|iperf"
to generate these results.
thanks for your help,
Willem de Bruijn
current project :
Fairly Fast Packet Filter (FFPF)
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2004-05-23 15:33 question regarding strange kernel stats under high (network) load Willem de Bruijn
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