Dualcore usage on gentoo-sources-2.6.26-r3

Boccaccio · Apprentice Joined: 19 Jul 2005 Posts: 286

Hi everyone!
I just emerged the new gentoo-sources-2.6.26-r3. Now that I run some computation, I found out, that it is done exclusively on one core of my T7300 while the other one is more or less idle (the app only manages to use one core) while on 2.6.25 and earlier, the job switched between the two cores which effectively kept everything cooler (and quieter). Is this a bug in 2.6.26? Or even some nice feature I just don't get the sense of?

thestick · Guru Joined: 07 Apr 2006 Posts: 531 Location: /dev/urandom

are you talking about building or just emerging gentoo-sources?
emerging will only unpack and move the sources to /usr/src/
building will use both of your cores if you

Boccaccio · Apprentice Joined: 19 Jul 2005 Posts: 286

No, I emerged the kernel, compiled it (still using the old one). Then I booted into the new one and did some calculations with mathematica. And these calculations only use one core instead of both (no matter which kernel I use). The kind of problem is, that with the old kernel, the job switched all the time between core 1 and core 2 while now the job is done only using core 1, say. In principle this is not problematic, but I think that due to this, this one core gets hotter so it must be cooled more, making the fan louder which I would like to avoid. Concerning the performace there is obviously no change between 2.6.25 and 2.6.26.

thestick · Guru Joined: 07 Apr 2006 Posts: 531 Location: /dev/urandom

oh, then i have no idea. you should probably check out the "Processor type and features" in menuconfig, they probably renamed a symbol/option or something.

Boccaccio · Apprentice Joined: 19 Jul 2005 Posts: 286

Well, I use CONFIG_X86_MINIMUM_CPU_FAMILY=6 and CONFIG_MCORE2=y now, and I have the impression, that after rather long periods of time, the core is switched. Maybe this is indeed the best solution how to deal with two core?!

eccerr0r · Posted: Tue Nov 25, 2008 11:48 pm Post subject:

It's more efficient if you have one thread to run it on one core (research "processor affinity"). It might be easier on the system to balance it between the two cores, but it's slower (just get a slower CPU instead!) and consumes *more* electricity overall since it takes longer.

As long as you run another process and it runs on the other core, you're fine.
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