> On Jul 21, 2016, at 8:54 AM, Neil Horman <nhorman at tuxdriver.com> wrote:
>
> On Wed, Jul 20, 2016 at 10:32:28PM +0000, Wiles, Keith wrote:
>>
>>> On Jul 20, 2016, at 3:16 PM, Neil Horman <nhorman at 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 at 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 at 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?
>>
> It may, but that seems to be reason to me to just set DPDK_MAKE_JOBS=0, and
> you'll get that behavior
Just to be sure, ?make -j 0? is not a valid argument to the -j option. It looks
like you have to do ?-j? or ?-j N? or no option where N != 0
I think we just use -j which gets us the 80% rule and the best performance
without counting cores.
>
> Neil
>
>> 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
