Re: [dpdk-dev] [PATCH] validate_abi: build faster by augmenting make with job count

["Wiles, Keith" <keith.wiles@intel.com>]

> On Jul 20, 2016, at 3:16 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
> 
> On Wed, Jul 20, 2016 at 07:47:32PM +0000, Wiles, Keith wrote:
>> 
>>> On Jul 20, 2016, at 12:48 PM, Neil Horman <nhorman@redhat.com> wrote:
>>> 
>>> On Wed, Jul 20, 2016 at 07:40:49PM +0200, Thomas Monjalon wrote:
>>>> 2016-07-20 13:09, Neil Horman:
>>>>> From: Neil Horman <nhorman@redhat.com>
>>>>> 
>>>>> John Mcnamara and I were discussing enhacing the validate_abi script to build
>>>>> the dpdk tree faster with multiple jobs.  Theres no reason not to do it, so this
>>>>> implements that requirement.  It uses a MAKE_JOBS variable that can be set by
>>>>> the user to limit the job count.  By default the job count is set to the number
>>>>> of online cpus.
>>>> 
>>>> Please could you use the variable name DPDK_MAKE_JOBS?
>>>> This name is already used in scripts/test-build.sh.
>>>> 
>>> Sure
>>> 
>>>>> +if [ -z "$MAKE_JOBS" ]
>>>>> +then
>>>>> +	# This counts the number of cpus on the system
>>>>> +	MAKE_JOBS=`lscpu -p=cpu | grep -v "#" | wc -l`
>>>>> +fi
>>>> 
>>>> Is lscpu common enough?
>>>> 
>>> I'm not sure how to answer that.  lscpu is part of the util-linux package, which
>>> is part of any base install.  Theres a variant for BSD, but I'm not sure how
>>> common it is there.
>>> Neil
>>> 
>>>> Another acceptable default would be just "-j" without any number.
>>>> It would make the number of jobs unlimited.
>> 
>> I think the best is just use -j as it tries to use the correct number of jobs based on the number of cores, right?
>> 
> -j with no argument (or -j 0), is sort of, maybe what you want.  With either of
> those options, make will just issue jobs as fast as it processes dependencies.
> Dependent on how parallel the build is, that can lead to tons of waiting process
> (i.e. more than your number of online cpus), which can actually hurt your build
> time.

I read the manual and looked at the code, which supports your statement. (I think I had some statement on stack overflow and the last time I believe anything on the internet :-) I have not seen a lot of differences in compile times with -j on my system. Mostly I suspect it is the number of paths in the dependency, cores and memory on the system.

I have 72 lcores or 2 sockets, 18 cores per socket. Xeon 2.3Ghz cores.

$ export RTE_TARGET=x86_64-native-linuxapp-gcc 

$ time make install T=${RTE_TARGET}
real	0m59.445s user	0m27.344s sys	0m7.040s

$ time make install T=${RTE_TARGET} -j
real	0m26.584s user	0m14.380s sys	0m5.120s

# Remove the x86_64-native-linuxapp-gcc

$ time make install T=${RTE_TARGET} -j 72
real	0m23.454s user	0m10.832s sys	0m4.664s

$ time make install T=${RTE_TARGET} -j 8
real	0m23.812s user	0m10.672s sys	0m4.276s

cd x86_64-native-linuxapp-gcc
$ make clean
$ time make
real	0m28.539s user	0m9.820s sys	0m3.620s

# Do a make clean between each build.

$ time make -j
real	0m7.217s user	0m6.532s sys	0m2.332s

$ time make -j 8
real	0m8.256s user	0m6.472s sys	0m2.456s

$ time make -j 72
real	0m6.866s user	0m6.184s sys	0m2.216s

Just the real time numbers in the following table.

processes     real Time   depdirs
     no -j             59.4s        Yes
       -j 8             23.8s        Yes
      -j 72            23.5s        Yes
        -j               26.5s        Yes

     no -j             28.5s         No
       -j 8               8.2s         No
      -j 72              6.8s         No
        -j                 7.2s         No

Looks like the depdirs build time on my system:
$ make clean -j
$ rm .depdirs
$ time make -j
real	0m23.734s user	0m11.228s sys	0m4.844s

About 16 seconds, which is not a lot of savings. Now the difference from no -j to -j is a lot, but the difference between -j and -j <cpu_count> is not a huge saving. This leads me back to over engineering the problem when ‘-j’ would work just as well here.

Even on my MacBook Pro i7 system the difference is not that much 1m8s without depdirs build for -j in a VirtualBox with all 4 cores 8G RAM. Compared to 1m13s with -j 4 option.

I just wonder if it makes a lot of sense to use cpuinfo in this given case if it turns out to be -j works with the 80% rule?

On some other project with a lot more files like the FreeBSD or Linux distro, yes it would make a fair amount of real time difference.

Keith

> 
> While its fine in los of cases, its not always fine, and with this
> implementation you can still opt in to that behavior by setting DPDK_MAKE_JOBS=0
> 
> Neil
> 
>>