How to increase maximum user cpu usage allowed on a multi core system?

[stan]

On Wed, 11 Mar 2015 16:36:43 +0000
Ian Malone <ibmalone at gmail.com> wrote:

> You may want to check the .NOTPARALLEL directive is not present
> http://www.gnu.org/software/make/manual/make.html#Parallel though I
> think that would simply prevent multiple processes.

This sounded like exactly the problem, but when I checked all the make
files in the kernel build tree, none of them had this directive.

> 
> To repeat, make -j N should be able to start N processes and they
> should not be subject to an overall limit other than hardware.
> (Incidentally, one process can use more than 100% if written to use
> parallelisation, you can often see jvm doing this.)

I took Martin's suggestion and checked the Gentoo take on this.  Your
experience is the general experience they had.  But there were some
people that didn't get that, and the suggestion they got was that the
make file had been written in such a way that it wouldn't allow the
request (the impression was *badly* written).  But, again, there were
many people saying they pegged all their cores at 100% when compiling
the kernel just by using make -j#.  There was lots of discussion of
what # should be, and even testing programs that people could use.  On
my box, I even see the kernel request -j6 on its own, but it still only
uses 1 core equivalent.  When I run a kernel compile with make -j, I
see dozens of processes created by make in htop, but they still only use
the equivalent of 1 core of cpu.

When I build firefox nightly with -j6, just at the end of the export
phase, and before the compile starts, I see all 6 cores maxed out.
Once the compile starts, it is back to a single core equivalent.  The
Gentoo users seemed to suggest that this was a flaw in the firefox
build process, though, and not the fault of the scheduler.

> Since I can't reproduce this problem I'm not sure what's causing it.
> If you really are finding make subprocesses limited to 100% cpu across
> the lot then maybe have a look to see if there are any cgroups limits
> active
> https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/ch01.html
> may also be worth running on the stock fedora kernel to test that
> it's not something that you've turned on in your custom kernel.

This sounds promising, and I have cgroups turned on in the config file,
but so does the standard kernel.  I also don't know how I would look
for cgroup configuration.  I'll do more research.

Thanks.