[olug] Kernel Compilation

[Vincent Raffensberger]

No, on a dual processor machine 4 should be best.  This just specifies
the number of gcc lines to process simultaneously.  I believe make waits
for each one to complete before starting a new one.  When that is
happening, idle cpu cycles are wasted waiting on disk access before
starting the new line. <-???  Since we're referring to a real
multi-tasking OS, this setting should help both single and smp systems,
but I would raise it even higher with more than two processors.

(from the make man page)

-j jobs
            Specifies  the  number  of jobs (commands) to run
simultaneously.  If there is
            more than one -j option, the last one is effective.  If the
-j option is given
            without  an  argument,  make  will  not  limit the number of
jobs that can run
            simultaneously.

Here's an experiment for you:  time one this way and then add another
alias like this:

alias gcc='gcc -03'

and time that one.  That's a good P6 optimization.  There are a few
others, but I think that one is the biggest.

Have you tried to optimize your disks with hdparm yet?  If you want to
start tweaking things for performance, there are a lot of things you can
do.  Many are simple changes to files in /proc and don't really require
a kernel re-compile.


Jason Ferguson wrote:
> 
> Ooooo, that was nice.  I slapped that one into my .bash_profile.  Gave me a
> MASSIVE decrease in compilation time for the sane package. However, since I
> have a 2 processor system, shouldnt I do 'make -j 2'?
> 
> Jason
> 
> Vincent Raffensberger wrote:
> 
> > >From what I've seen, a little optimization for make gives a huge
> > improvement (especially for smp).  Try this before you start compiling:
> >
> > alias make='make -j 4'
> >
> > I've used the "-03" option for egcs before, which should help, but I'm
> > never in that much of a hurry.  "info egcs" will show you all the
> > optimizations.  You could also recompile egcs, since it's probably just
> > a i386 optimized binary from installation.
> >
> > Jason Ferguson wrote:
> > >
> > > Okay, yes, I do know how to compile a kernel, thank you very much. :)
> > >
> > > However, my question: is it possible or even advisable to use processor
> > > optimizations when compiling a kernel?
> > >
> > > I ask this because, frankly, Im one of those geeks who likes to wring
> > > the last ergs of performance out of my machine.  If I have a P3
> > > processor, why shouldnt my stuff be optimizaed for it (even if I only
> > > gain 10% or so?).
> > >
> > > What do you guys think?
> > >
> > > Jason
> > >
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