Chapter 3. Bandwidth and Processing Power

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3.2.3.2.1. Upgrading the CPU

The most straightforward approach is to determine if your system's CPU can be upgraded. The first

step is to see if the current CPU can be removed. Some systems (primarily laptops) have CPUs that

are soldered in place, making an upgrade impossible. The rest, however, have socketed CPUs, making

upgrades possible   at least in theory.

Next, you must do some research to determine if a faster CPU exists for your system configuration.

For example, if you currently have a 1GHz CPU, and a 2GHz unit of the same type exists, an upgrade

might be possible.

Finally, you must determine the maximum clock speed supported by your system. To continue the

example above, even if a 2GHz CPU of the proper type exists, a simple CPU swap is not an option if

your system only supports processors running at 1GHz or below.

Should you find that you cannot install a faster CPU in your system, your options may be limited to

changing motherboards or even the more expensive forklift upgrade mentioned earlier.

However, some system configurations make a slightly different approach possible. Instead of replacing

the current CPU, why not just add another one?

3.2.3.2.2. Is Symmetric Multiprocessing Right for You?

Symmetric multiprocessing (also known as SMP) makes it possible for a computer system to have

more than one CPU sharing all system resources. This means that, unlike a uniprocessor system, an

SMP system may actually have more than one process running at the same time.

At first glance, this seems like any system administrator's dream. First and foremost, SMP makes it

possible to increase a system's CPU power even if CPUs with faster clock speeds are not available  

just by adding another CPU. However, this flexibility comes with some caveats.

The first caveat is that not all systems are capable of SMP operation. Your system must have a moth 

erboard designed to support multiple processors. If it does not, a motherboard upgrade (at the least)

would be required.

The second caveat is that SMP increases system overhead. This makes sense if you stop to think

about it; with more CPUs to schedule work for, the operating system requires more CPU cycles for

overhead. Another aspect to this is that with multiple CPUs there can be more contention for system

resources. Because of these factors, upgrading a dual processor system to a quad processor unit does

not result in a 100% increase in available CPU power. In fact, depending on the actual hardware, the

workload, and the processor architecture, it is possible to reach a point where the addition of another

processor could actually reduce system performance.

Another point to keep in mind is that SMP does not help workloads that consist of one monolithic

application with a single stream of execution. In other words, if a large compute bound simulation

program runs as one process and with no threads, it will not run any faster on an SMP system than on

a single processor machine. In fact, it may even run somewhat slower, due to the increased overhead

SMP brings. For these reasons, many system administrators feel that when it comes to CPU power,

single stream processing power is the way to go. It provides the most CPU power with the fewest

restrictions on its use.

While this discussion seems to indicate that SMP is never a good idea, there are circumstances in

which it makes sense. For example, environments running multiple highly compute bound applica 

tions are good candidates for SMP. The reason for this is that applications that do nothing but compute

for long periods of time keep contention between active processes (and therefore, the operating system

overhead) to a minimum, while the processes themselves keep every CPU busy.

One other thing to keep in mind about SMP is that the performance of an SMP system tends to

degrade more gracefully as the system load increases. This does make SMP systems popular in server

and multi user environments, as the ever changing process mix impacts the system wide load less on

a multi processor machine.