[LEDE-DEV] [PATCH] sdk: automatically use all CPU cores for xz

[Jonas Gorski]

On 18 August 2017 at 15:06, Karl Palsson <karlp at tweak.net.au> wrote:
>
> Bjørn Mork  <bjorn at mork.no> wrote:
>> This looks yucky. Experimenting a bit, I see that the result
>> with
>>
>>  a) -T 0 depends on multi-core vs single-core
>>  b) -T 1 is always different from the output of -T x where x > 1
>>  c) -T x where x > 1 is independent of both x and the actual number of
>>     cores
>>
>> So you will not get reproducible results with either "-T 0" or
>> "-T <value from make -j>".
>
> Sure, but -T 0 will be ok for _any_ computer with more than one
> core. Which is enough of them now, and enough for people doing
> builds that care about reproducibility, and certainly enough of
> them to appreciate the dramatically sped up builds.

To get this discussion further I, if getting the -j value is far from
easy, especially in a portable way (as googling suggest), I suggest
adding a config option for enabling parallel XZ compression, either as
a bool or directly as a integer for the amount of threads to use,
defaulting to n/1. The int option is probably the best as it gives the
most control over it.

Then those that case about speed can enable it/set it 0, and those
that want to use their PC for other things at the same time can leave
it at 1 or an appropriate value so it doesn't take over the whole
system during compression.


Regards
Jonas