udev performance
Harald Hoyer
harald at redhat.com
Tue Sep 11 15:40:27 UTC 2007
William Cohen schrieb:
> Harald Hoyer wrote:
>> Harald Hoyer schrieb:
>>> 44.1% (1,6s) with /sbin/modprobe
>>
>> modprobe is parsing its configuration/dependency files every time it
>> is called.
>>
>>> 12% (0.44s) with 60-net.rules
>>
>> I am sure 60-net.rules does not have to call
>> /etc/sysconfig/network-scripts/net.hotplug for _every_ "net" event.
>>
>>
>
> A while back I did some experiments with systemtap and found that
> modprobe was doing a linear search through modules.deps:
>
> http://sourceware.org/ml/systemtap/2007-q1/msg00140.html
>
> I wrote a script that would prepend the modules that are actually used
> to the beginning of modules.dep to reduce the average length of search.
> This reduced the amount of data read (and time spent waiting for I/O)
> and slightly reduced the time to boot the machine. Bootchart samples
> process state periodically. Below is some of the data extracted from the
> bootchart samples:
>
> all states D state
> modprobe modprobe
> samples samples
> normal modules.dep 120 73
> reordered modules.deps 63 27
>
> Having to linearly through 250K of text in modules.dep each time a
> module is loaded doesn't seem very efficient.
>
>
> -Will
>
Problem is, that most of the modprobes with a modalias are not existent and so every line is parsed.
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