[Beowulf] Clustering VPS servers

Mark Hahn hahn at mcmaster.ca
Sun Mar 24 10:22:04 PDT 2013


> What I am not understanding is the difference between using a monolithic
> style kernel with everything compiled in vs. modules. Is there a lower
> memory footprint if modules are used.

modules do have a marginally higher overhead (as well as potentially 
a slightly slower layout in memory.)  but if your system has only the 
features/drivers you need, it won't make any real difference whether 
monolithic or modular.  the real issue is that a distro kernel will 
have a lot of stuff compiled into it that you don't need, and will 
probably also be compiled for a generic x86.

but the memory used by modules tends to be quite small - do lsmod,
and see that they're mostly something like 20KB, with occasional
big ones (graphics drivers, etc) that don't usually break 1MB.
4 MB on my 4GB laptop (fedora 17).  on a centos 6 cluster node 
with lots of pointless modules, it's 8MB out of 32GB.

so memory really isn't the issue.  it's not clear to me whether there
are other factors that would produce noticable cpu/performance benefits.
compiling for cpu families sounds plausible, but since the kernel is 
rarely compute-bound.  (the previous mention of using updated drivers 
makes a lot more sense.)


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