user:sys time ratio

Poul-Henning Kamp phk at
Sun Nov 30 06:38:56 PST 2003

In message < at>, Colin Percival
>At 15:30 30/11/2003 +0100, Poul-Henning Kamp wrote:
>>In message < at>, Colin 
>>  writes:
>> >   When running `make buildworld`, I see large amounts of sys time; eg, 27
>> >minutes user & 14 minutes sys for building 5.2, or 14 minutes user & 10
>> >minutes sys for building 4.9.  I expected the ratio of user:sys to be much
>> >larger than this, and mailing list traffic indicates that a 4:1 ratio is
>> >typical.
> >I've seen UNIX systems have "typical" system/user splits from 1/9 to 9/1
>>it all depends on what you're doing.
>   Sure, but buildworld is a fairly well-defined benchmark; I wouldn't 
>expect to see such a large difference when running exactly the same code on 
>different systems.

The amount of system time depends on a lot of environmental factors.

For instance on my amd64/SMP, the vnode pool is mis-sized, so the the
namecache does not reflect what is actually already in RAM.  The result
is a fair bit of system time wasted instantiating vnodes from cached
inode diskblocks.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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