[distcc] homogeneous environments
Robert W. Anderson
anderson110 at poptop.llnl.gov
Tue May 5 16:37:27 GMT 2009
Fergus Henderson wrote:
>
>
> On Thu, Apr 30, 2009 at 9:07 PM, Robert W. Anderson
> <anderson110 at poptop.llnl.gov <mailto:anderson110 at poptop.llnl.gov>> wrote:
>
> Fergus Henderson wrote:
>
> The include server could be the bottleneck. What's the CPU
> usage for the include server process?
> Or it could be disk I/O. Try iostat or vmstat to profile that.
>
>
> After some more experimentation, I think I may have a clue what's
> going on here. I think I may be getting bound up in context
> switching costs, both in my single node performance and on localhost
> using distcc.
>
> On a single node:
>
> -j4: 24 million context switches @ 10us = 4m
> -j8: 96 million context switches @ 10us = 16m
> ...
>
> I don't understand why doubling the job count increases context
> switching by 4x. Any insights appreciated.
>
>
> You mentioned earlier that your host has four processors.
No, I mentioned a few times that it has 16 processors.
Thanks,
--
Robert W. Anderson
Center for Applied Scientific Computing
Email: anderson110 at llnl.gov
Tel: 925-424-2858 Fax: 925-423-8704
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