hugemem? smp?

[Rick Stevens]

On Wed, 2006-07-19 at 15:04 -0700, chuck lawrence wrote:
> thanks to good-hearted folks here, I've been using the hugemem kernel to 
> address 8gb of ram on my dual opteron rh es 3.0 servers.
> 
> one user has reported that the cpu load balancing seems different on 
> these, compared to other servers with generic kernels (and less ram). 
> in particular, he says the hugemem systems pile more processes onto the 
> first processor, before moving on to the 2nd.
> 
> is hugemem multi-processor by default?  is there something else I should do?

Yes, hugemem is multiprocessor.  The easiest way to check is:

	# cat /proc/cpuinfo

You'll see multiple CPUs if you have multiple CPUs, hyperthreading CPUs
or multiple hyperthreading CPUs (essentially each hyperthread is treated
as a CPU).  So, a two-processor SMP machine with two standard Xeons
would show 4 CPUs.  A two-processor SMP, multicore, hyperthreading
machine would show 8 CPUs.

As to the load balancing...the memory model shouldn't cause a
significant difference.  CPU0 generally will be a bit busier since it
runs the scheduler.  If you don't use the APICs ("noapic" on the boot
command line), CPU0 will do almost all the I/O and it'll be busier
still.  The thing with smaller memory models is that you may end up
swapping more or doing more context switches and the differences between
the CPU loads can be masked by that.

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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
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