Vincent Sweeney wrote:
>
> Naturally I would really like to know where / what is using up all this
> system cpu so I would like to try profiling the kernel as I'm sure this is a
> pure kernel network layer performance issue but I have no idea where to
> start so does anyone have some advice / tips on where I should start?
Yes, profiling the kernel is clearly the next step. And it's
really easy.
1: If possible, rebuild your kernel with as few modules as possible.
Current profiler doesn't cope with code which is in modules.
2: If you're on uniprocessor, enable the "Local APIC support on
Uniprocessors" option. This allows higher-resolution profiling.
3: Arrange for the kernel to be provided the `profile=1' boot
option. I use
append="profile=1"
in /etc/lilo.conf
After a reboot, the kernel is profiling itself. The overhead is
really low.
4: Bring the server online and wait until it starts to play up.
Now we can profile it. I use this script:
mnm:/home/akpm> cat $(which akpm-prof)
#!/bin/sh
TIMEFILE=/tmp/$(basename $1).time
sudo readprofile -r
sudo readprofile -M10
time "$@"
readprofile -v -m /boot/System.map | sort -n +2 | tail -40 | tee $TIMEFILE
echo created $TIMEFILE
Let's go through it:
readprofile -r
This clears out the kernel's current profiling info
readprofile -M10
This attempts to set the profiling interval to 10*HZ
(1000 Hz). This requires a local APIC, and a recent
util-linux package. Not very important if this fails.
This command also cleans out the kernel's current
profiling info (it's a superset of -r).
time "$@"
Runs the command which we wish to profile
readprofile ...
Emits the profile info, sorted in useful order.
You must make sure that /boot/System.map is the
correct one for the currently-running kernel!
So in your situation, the command which you want to profile isn't
important - you want to profile kernel activity arising from
*existing* processes. So you can use:
akpm-prof sleep 30
Please send the results!
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This archive was generated by hypermail 2b29 : Thu Jan 31 2002 - 21:00:46 EST