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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