topic Re: CPU usage in Operating System - HP-UX

CPU usage

sheevm — Wed, 19 Dec 2007 21:54:18 GMT

We are using rp8420 with 4 CPU's.

I need some help in interpreting the CPU performance. Can we say that the system is 4 times powerful because 0f 4 CPU's versus one?

For example: if one processor system mcan process 100 trnsaction then 4 processor can process 400 transcation.

Please excuse me if my question is not clear.

Thanks

Re: CPU usage

Hasan Atasoy — Wed, 19 Dec 2007 21:58:05 GMT

hi kesh ,
if your application is a multithreaded app then we can 4 cpu machine is powerfull than 1 cpu machine. but if your application single thread app then we cannpt say it. it is a bit diffucult to say 4times faster .

Hasan.

Re: CPU usage

Sandman! — Wed, 19 Dec 2007 21:58:39 GMT

>For example: if one processor system mcan process 100 trnsaction then 4 >processor can process 400 transcation.

No the scale-up is not linear owing to synchronization and coherency issues.

Re: CPU usage

Tim Nelson — Wed, 19 Dec 2007 22:01:01 GMT

In general 4 is 4 times 1.

but........
In reality not all servers, OSs and software applications scale 1 for 1 with CPU additions, but this typically only applies to over 8,12,16,32,64 or more CPUs. Check the latest TPC benchmarks on the WWW.

Also, if your application is single threaded then it will only be able to use 1 CPU at a time anyway and all the other CPUs do is to allow other processes CPU time.

Re: CPU usage

TwoProc — Wed, 19 Dec 2007 22:26:11 GMT

Well, like most things, it depends.

I would say yes, for a purely cpu intensive process. However, almost no-one has such a thing, most people run business apps, which bring up and down memory resources, disk resources, network resources, etc.

An example of a purely cpu intensive process would be calculating pi.

So, if you added 4 processors would you calculate pi 4x faster? No, unless you were running a multiprocessing pi calculation engine which would use more threads to work. If you did have a multiprocessing pi calculator, then yes, providing you didn't run out of memory, you should run 4x faster.

Or, if you ran 4 separate pi calculators simultaneously, then you'd probably run roughly 4x faster on a 4 processor system than on a 1 processor system (disregarding system processing time).

Re: CPU usage

Dennis Handly — Thu, 20 Dec 2007 06:53:51 GMT

>TwoProc: providing you didn't run out of memory, you should run 4x faster.

Even if you didn't run out of memory, any memory or cache access in different processes could slow the others down some.