On Sat, 8 May 1999, Thomas Wouters wrote:

> > > Are you so sure? 2x SMP on intel means about 30% performance increase,
> > > if you are lucky. SMP on intel can even _slow you down_ for certain
> > > kind of loads, and web server may be exactly this kind of load.
> 
> > That seems _highly_ unlikely, and my own experience is contrary to this.
> > Are you sure about this?
> 
> It depends highly on the kind of website you're serving. If you are mostly
> serving straight files (either html files or other data) your cpu will be
> hardly used (relatively speaking) and the bottleneck will be one of the
> network, your disks or the throughput your machine can manage. Adding CPUs
> will have little impact in such a case. If, however, the machine is used to
> run a lot of scripts that do complicated things (and dont do too much i/o,
> relatively speaking) the CPU might help.

That's not what my response was about. The person I was responding to had
stated (as you can see at the top) that there is a 30% performance
increase with SMP. No stipulations about I/O-based bottlenecks or
too-small RAM or anything. I want to know where he got those numbers from.
Further, I would like to know of any real-world situations where he has
actually seen performance decrease on a SMP system. In other words, I want
evidence.

I understand that when you increase the computing power of a system you
often have to increase its available resources. Bigger power supply,
faster disks, more RAM...no problem. But an example system gets only a 30%
increase in capacity once you've added a CPU and this is a result of not
enough RAM, you don't then say in a public forum it "means about [a] 30%
performance increase."


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