🚀 go-pugleaf

George Bell wrote:
> warr wrote:
<snip>
> 
> 
> While I generally agree that dual CPU may be inappropriate, this is an 
> inaccurate statement.  The allocation of CPU resources is a function of 
> the os, not the tasks running(and thus the software).  Since Linux can 
> support SMP - symetric multiprocessor( each processor gets as much 
> "work" as the other ), then twice as much CPU time is available to the 
> system and the performance is twice as great, period.
<snip>

Remarkable amount of cock and bull being put forward in this thread 
isn't there?

Here are some facts (Assume SMP system with same CPU as a uni-processor):

- No application that runs in Linux can specify what cpu it will run 
on in an SMP system. There is (was ?) a tool around that could force 
the app to run on a certain cpu in an SMP system...In reality, the 
Kernel will almost always know better how to schedule processes.

- An application that is single threaded will likely perform slightly 
worse  in absolute terms on a SMP system than on a uni-processor 
system if the overall load is next to nothing. Why? The Linux SMP runs 
a copy of the Kernel on each CPU, and runs an overhead to manage the 
SMP environment. A uni processor system runs a single copy of the 
Kernel on one CPU with no SMP overhead.

	ie SMPload = KernelOverhead + SMBoverhead + process
            UNIload = KernelOverhead + process

HOWEVER as a result of the fact that a Linux system typically has more 
than one process running at a time, it is likely that since the SMP 
aware Kernel(s) are load balancing between cpu's, the single threaded 
application will actually perform better on a SMP system than on 
uni-processor machine because it is running on a single cpu that has 
less load - the single thread gets more cpu time to do it's job. In 
fact the theoretical no-load environment is completely unrealistic.

- The applications that are "written to take advantage of SMP systems" 
are simply multi-threaded. Multi-threaded applications are *no big 
deal*, and are still an advantage on uni-processor machines.

BTW, the performance isn't twice as great on a SMP system. There is 
overhead, resulting in SMP system being something less than twice the 
performance.


In a nut shell, a SMP Linux system running on 2X 1800 Athlons will 
always  be superior to a uni-processor 1800 AThlon machine due to the 
fact that a typical Linux system has many processes running 
(Multi-threaded or not). But the performance advantage of 
multi-threaded app is *much* greater than a single threaded app on a 
SMP system.


Cheers,
Michael