Dual core + task manager = question

Golden Ape · 4 Apr 2006 at 22:14

Hi, I've just bought a nice new dual core centro laptop, which is working fantasticallly. However I've notice something odd in taskmanger. As expected if I run a single process at full wack (e.g. compressing lots of files, running a matlab simulation) then the cpu usage jumps upto 50% or there abouts. I assumed this meant one of the processors was working at 100% on the task and the other was idling. However when I go to the 'performance' tab in taskmanger I see two cpu graphs, one for each core, but both are hovering around the 50% mark. What's going on?

marc2003 · 4 Apr 2006 at 22:20

the load is being shared between the the 2 cores :confused:

what's hard to understand about that....

Otacon · 4 Apr 2006 at 23:29

You're being bound by some other bottleneck. On a laptop, probably disk i/o.

dave_a141 · 4 Apr 2006 at 23:38

It happens to me with my Opteron 165, no matter what you do both stay on 50%.
Two instances of prime, multithreaded 3d rendering, the system behaves as if its fully loaded but task manager reports 50% on each

EDIT: weird, I just checked and mines on 100% both cores, never seen that before, always used to be 50% :confused:

Have you got the latest updates/drivers etc?

Golden Ape · 5 Apr 2006 at 00:23

Thanks for all the input. I guess I'm still suprised, from what I'd been led to belive a single threaded process (which both of the examples are) should remain bound to a single core. Surely having a process swap between cores would introduce an addittional overhead? So in practise a single core should run at 100% and the other should run at 0% (depending on what else is running). Since this isn't happening I obviously belive the wrong thing but I'm still quite suprised.

Otacon: I suspect it isn't an additional bottleneck as the balance is too perfectly 50% (that and the fact that I'm luck enough to have a laptop with a nice fast 7200rpm disk)

Golden Ape · 5 Apr 2006 at 09:44

marc2003. Well I stand 100% corrected. It does seem that the process is switching between the cores. In task manager if I right click the process it's possible to set the affinity so that it only runs on one core. Doing this, as you might expect, causes the process to run at 100% on that core and to leave the other one alone. Though I'm still suprised the it swaps between the cores at all - I just don't see what the advantage would be.

NathanE · 5 Apr 2006 at 11:46

It is swapped core by the kernel's scheduler and it only does it if there is performance that outweighs the cache flush penalty to be gained.

50% is just the way Windows reports 100% on a dual core/CPU system. Nothing to worry about