Question about single-threaded performance

[manarak]

I got a question about CPU/System performance.

What is the perofrmance of dual cores compared to single cores of the same clock speed for single-threaded applications?

What if we compare the single thread performance of strongest setups for single core, dual core and 2x2 ?
Can a 2x2 system run as fast as single/dual cores?

 

[mkaibear]

Assuming all cores are the same architecture and the same clock speed,

For strict single-threaded applications, the single core and the dual core will run at the same speed.

For strict dual-threaded applications, the single core will run at approximately half the speed of the dual core.

A 2x2 system will run a single-threaded application at the same speed as the dual-core and the single core, will run a dual-threaded application at the same speed as the dual core, and will run a quad-threaded application approximately twice as fast as the dual core would (and hence 4 times as fast as the single core would).


In the real world, of course, there is not really any such thing as a "strict single-threaded application".

 

[niz]

Assuming all cores are the same architecture and the same clock speed,

For strict single-threaded applications, the single core and the dual core will run at the same speed.

For strict dual-threaded applications, the single core will run at approximately half the speed of the dual core.

A 2x2 system will run a single-threaded application at the same speed as the dual-core and the single core, will run a dual-threaded application at the same speed as the dual core, and will run a quad-threaded application approximately twice as fast as the dual core would (and hence 4 times as fast as the single core would).


In the real world, of course, there is not really any such thing as a "strict single-threaded application".

Whan an app is running its not the only thing using the processor. Other background apps, drivers and operating system services are also grabbing CPU time.

Even if you have a single-threaded app it will get more cpu time on a multi-core proc. (so appear to run faster) because all the other stuff that would normally have to interrupt your app to run on the same cpu core can now use the other core instead.

 

[mkaibear]

>Even if you have a single-threaded app it will run faster on a multi-core proc. because it gets interrupted less, as the kernel can also run all the other stuff on the cpu core your single-threaded app is not using.



Yes, thank you Niz... hence my comment of "In the real world, of course, there is not really any such thing as a "strict single-threaded application"."

 

[drcroubie]

just for comparison, consider superPI, which only ever runs on 1 core at once:
a Turion x2 TL-50 (1.6GHz) has exactly the same times as a sempron 2800+ (1.6GHz) (1M@52s). then my X2 3800+ (2.0GHz) comes in at 42s (overclocked to 2.25GHz gets 36s), and a 3800+ (2.4GHz) gets 33s.
(rough comparison, all with comparable ram speeds etc, all am2/s1,
all brand new systems, no other crap loaded other than graphics/ethernet drivers.)


but yeah, in the real world, all those damn virus scanners, firewalls, (and everything else required for windoze to survive), plus IMs, torrents, whatever, do make dual-cores worth a lot more than higher single-core clockspeed....