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

[Mark Knecht]

On Fri, Sep 30, 2011 at 3:09 PM, Neil Bothwick <neil@××××××××××.uk> wrote:
> 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

OK, my bad for confusing the two. Currently make.conf in the chroot says:

MAKEOPTS="-j3"

and when I run emerge in the chroot it's typically

emerge -DuN -j2 @world

so I think that's about right, or would hope it is anyway. If you see
a problem please let me know.

I'll add the ionice stuff this weekend and see how it goes.

Thanks,
Mark