[CMake] Does Makefile generated by CMake support make -jN?

[Andrew Melo]

On Tue, Jul 12, 2016 at 10:48 PM, Chaos Zhang <zcsd2012 at gmail.com> wrote:
> Thanks for your reply Raymond, by 'If you got 96% both times, then I would
> say there's a problem.', did you mean if make performed like this, it means
> this project can't use make -jN?

If "make -j1" and "make -j8" ran in the same amount of time, there
would be a problem. Since "make -j1" uses 96% CPU and "make -j8" uses
690% CPU, it implies that the "-j" options make compilation time
scale, which is what you want.

> BTW, does CMake support some options to
> turn on hardware acceleration?

What do you mean by "hardware acceleration"?



>
> Raymond Wan-2 wrote
>> Hi Chao,
>>
>>
>> On Wed, Jul 13, 2016 at 10:54 AM, Chaos Zhang <
>
>> zcsd2012@
>
>> > wrote:
>>> I was trying to compile my project using CMake, after CMake generated
>>> Makefile.
>>> I used `/usr/bin/time -v make` to make the Makefile,  got the result:
>>> 'Percent of CPU this job got: 96%'.
>>> Then i used `/usr/bin/time -v make -j8` to make the Makefile, the result
>>> of
>>> CPU used is  'Percent of CPU this job got: 648%'.
>>> So i wonder if Makefile generated by CMake support make -jN, BTW my CPU
>>> is
>>> I7-4790, and after i use 'cat /proc/cpuinfo', there are 8 processors.
>>
>>
>> I'm not sure what you are asking...
>>
>> You ran make with -j 8 and you got a percentage greater than 96% ...
>> this implies that the Makefile does support -jN, doesn't it?  If you
>> got 96% both times, then I would say there's a problem.
>>
>> Is what you're wondering why it is 648% and not 800%?  I think that
>> depends on the dependencies in your Makefile.  It's possible that some
>> of them depend on each other in such a way that 8 parallel threads is
>> not possible.
>>
>> Also, I can't remember the value returned by /usr/bin/time -v, but I
>> guess 648% is the average and not maximum.  So, perhaps there are
>> parts within the Makefile that only one thread could be used and then
>> it gets averaged out?
>>
>> Ray
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Andrew Melo