Re: [gentoo-user] Limit number of cores used by emerge?

[Neil Bothwick]

On Fri, 30 Sep 2011 11:15:16 -0700, Mark Knecht wrote:

> > If your MAKEOPTS is -j3 then it's not going to use more than 3 cores
> > at a time but it will touch all 12 cores throughout the process
> > because of the normal load balancing. If you want it to use only 3
> > specific cores, you would need to set the processor affinity (usually
> > done using the "taskset" command from sys-apps/util-linux).

> My experience with -j3 is not that it limits emerge to 3 CPU cores but
> rather it limits emerge to running 3 _jobs_. There's a big difference.
> 1 job can use 12 cores if gcc spawns a lot of stuff in parallel, which
> in my experience it does. It's this parallel spawn running up to 12
> cores in use which causes the machine to lag. Even when not setting
> the -j option at all which results in a single package being emerged
> at one time, I often use 6-12 cores in use for short periods of time
> as gcc builds that package.

That's the --jobs option for emerge. The suggestion was to set the -J
option in MAKEOPTS, which tells GCC how many compilation threads to run
at once, and that's one core per thread. You'll also need to set -j 1 for
emerge, which will also reduce the amount of disk thrashing that can
happen when two package hit unpack at the same time.


-- 
Neil Bothwick

If at first you don't succeed, skydiving is not for you.