Hyperthreading and Child Processes

[Matt Kettler]

At 01:53 PM 4/5/2004, Jason Burzenski wrote:
>Does anyone else use Xeon processors with hyperthreading enabled?  This
>has the effect of doubling the CPUs capacity.  The kernel reports each
>hyperthreading cpu as 2 cpus and I believe treats them as such.
>
>If I am running a dual xeon (2 real cpus, 2 virtual cpus) should I be
>running 20 MS processes or 10?  100Kmsgs/day running SA and 1 CL virus
>scanner.

I suspect you mean 2 real, 4 virtual.

The reality of hyperthreading isn't quite a doubling of CPUs, although it
is an improvement. Within HT the two virtual CPUs per real processor share
a common cache, and a common set of execution units, etc, which will limit
their thruput.

I'd suggest experimenting with values between 10 and 20..

Intel's fairly optimistic estimates put HT as a 30% increase in "server
benchmark tests", so I'd suggest starting at 13 processes based on that.
This may turn out to be slightly optimistic, but as long as you have enough
ram to support all the processes (15 at about 24mb each = 360mb)  it should
not be far enough off to cause noticeable degradation.