Re: Getting Number of CPU(-core)s and giving it as the --jobs argument to GNU Make

[Peter Dyballa <Peter_Dyballa@Web.DE>]

Am 11.09.2007 um 22:20 schrieb Dieter Wilhelm:

> That's a bit confusing, I thought I had *one* processor with *two*
> cores and the content in /proc/cpuinfo claims two processor, 0 and 1
> with two cores, respectively, where am I wrong?

HT – hyper-threading (parallel pipelines and parallel memory buses).  
Many modern intel CPUs claim they are two (Xeons are four, or even  
eight, I think). They are right, somehow: mostly you can assume that  
in your case four commands are (can be) executed at the same time.  
For your PC 'make -j 4' will improve compilation time. So doing in bash

	cores=`grep cores /proc/cpuinfo | wc -l`
	if [ $cores -eq 0 ]; then cores=1; fi
	procs=`grep processor /proc/cpuinfo | wc -l`
	thrds=`expr $cores \* $procs`

or in (t)csh

	set cores=`grep cores /proc/cpuinfo | wc -l`
	if ($cores == 0) set cores=1
	set procs=`grep processor /proc/cpuinfo | wc -l`
	set thrds=`expr $cores \* $procs`

would determine how many compilation threads can be executed in  
$thrds. And it should also work when the CPU has no core ... Solaris,  
AIX, HP-UX, IRIX ... have their own commands.


Anyway, a modern GNU make is able to determine by itself what's best.  
This is done via 'make -j' without a limiting number.

--
Mit friedvollen Grüßen

   Pete

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