Dual-Core and Quad-Core performance question

[Burke, Thomas G.]

I can't talk about the diffwrent systems specifically, but I can say this:

1). The multi-core systems should be slightly faster that the multiple single-core systems.  This is because the big bottleneck is "getting on the bus.". Memory access times for shared memory resources will be required to go out to main memory, which runs at approx 1/8 the speed of the processor.  This, of course, assumes that the data gets held in a common location, and the programs looking at that common location actually need that data.  Wh( the speed difference might be mosrt likely depends on the applicatron(s)

2). Speed p-up over a single core/processor - if the appplication is written to take advantage of multiple processors, the speed-up should be pretty good, but less than 100%.  If the process is a single-processor architecture, 25% or seems about right.  This is because the OS will run on one CPU/core and parse out tasks to the CPU/core with the most available resources.  Thus, on a dual-core system, the program may get 100% of the resources on 1 core while the OS resides on the other.  If the process coul support multiple execution threads, one of those might be on an otherwise empty processor, burt the other mustr share resources with the OS.  With 3 processors, say, a single-stringed app would see the same (maximum) speedup as with the dual-core system, but a multi-threaded system might see as much as 200%, but less than 300% speedup.

This all assumes, of course, that memory latencies and such don't overwhelm the gains from having multiple processors - at some point there becomes a point of diminishing returns.

     -Tom

I'm not at my desk, but I can be reached at 443-603-7308

----- Original Message -----
From: redhat-list-bounces at redhat.com <redhat-list-bounces at redhat.com>
To: General Red Hat Linux discussion list <redhat-list at redhat.com>
Sent: Mon Feb 25 15:42:06 2008
Subject: Dual-Core and Quad-Core performance question

Hello: 
        Can anyone point me to some information about the performance
differences of say the following systems. 

A) 4 Single-Core CPUs running at 3.0GHz 

B) 2 Dual-Core CPUs running at 3.0GHz 

C) 1 Quad-Core CPU running at 3.0GHz 

Everything else being the same, that is 4GB of memory, disk, etc... 

        The reason I ask, is I have been told that a Dual-Core System
will only give about a 25% performance improvement over 1 Single-Core
system. That is not it is not twice as fast.

---- 
Thanks: 
Jack Allen 


        

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