On Fri, Apr 3, 2020 at 5:26 PM Chris Johns <chr...@rtems.org> wrote: > On 2020-04-04 07:57, Joel Sherrill wrote: > > How does rtems-bsp-builder calculate the amount of parallelism to use? > > The option is documented here ... > > > https://docs.rtems.org/branches/master/user/tools/bsp-builder.html#cmdoption-jobs > > and is ... > > --jobs > > The jobs options where the format is build-jobs/make-jobs. The default > is 1/num-cores where num-cores is the operating system reported number > of cores. >
What's the definition of build job vs make job? Is make jobs equivalent to N in make -jN? > > > I ask because I have realized that I selected jobs=6/12 on a very beefy > > machine with 12 cores and 32 GB RAM. The main test machine I use is 8 > > cores/32 GB RAM. But the slowest ones are old with 4 cores/4 GB RAM. > > They are hitting the swap space. All have SSDs. > > > > Should I drop the --jobs parameter? Will the script select a decent load > > automatically? The machines are essentially dedicated to testing. > > You will need a --jobs option or the machine will not be fully loaded. > You need to find a balance between the number of parallel BSPs that are > built at once and the number of parallel build jobs each BSP makes runs. > > The critical factor is the amount of bootstrap and configure time. This > is a single core task and if you use the default a lot of the build time > the machine is basically idle. > But if you go too high, the number of compiles will swamp a machine without a huge amount of memory. So the 4 core/4 GB machines probably would be something like --jobs=2/4. if that's two bsp builds in parallel with a -j4. That generally gives you a 2x factor on processes which is close to the old school rule of the -jN number should be between 1.5 and 2 times the number of cores as long as the RAM and disk subsystem could handle it. That tends to overlap IO and computation. Maybe the default should be (roundup(cores)/2) instead of 1. Temporarily I may have to add a jobs option to my script and hand-tune it to the machines I am testing on. > There is no way I know of to automatically find this balance for all the > different types of host machines. > > Chris >
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