Re: [gentoo-user] is multi-core really worth it?

["J. Roeleveld" <joost@antarean.org>]

On Wednesday, November 22, 2017 2:12:31 PM CET Raffaele Belardi wrote:
> Jeremi Piotrowski wrote:
> > That being said: if you do a world rebuild you will have lots of packages
> > that spend ~40 seconds doing their autoconf run, only to build 2-3 sources
> > files. On an 8-core machine at work, I get good results using parallel
> > emerge jobs (emerge -jX). For your 6-core AMD CPU (assuming it actually
> > has 12 threads) I'd start with 'emerge -j3' and MAKEOPTS='-j12 -l16'.
> > That should get you a nice speedup, but may require a bit more ram.
> 
> emerge -j3 is something I did not think of, I'll try it. But won't that
> break portage's carefully crafted package dependencies? I suppose you could
> get occasional build failures?

No, it won't.
If it has multiple packages that can be built (taking dependencies into 
account) it will. If all packages in the queue are waiting for a single 
package to be installed, all those will wait till that package is finished.

> I'm using MAKEOPTS=-j7, I thought 2 threads per CPU (hyperthreading?) was an
> Intel thing only.

I thought so too.

Don't forget to add the "load-average" option to both, otherwise there is a 
very likely chance you will have 3 * 7 = 21 build processes running at the 
same time.

Also, I have had situations where using "-j" actually caused some issues where 
it was picked up by the wrong process or it has a different meaning for some 
other process. Specifying the long version (--jobs) has been reliable for me.

--
Joost