On 25-11-18, Segher Boessenkool via cfarm-users wrote: > On Sun, Nov 25, 2018 at 01:14:31PM +0100, Stefan Ring via cfarm-users wrote: > > On Sun, Nov 25, 2018 at 10:25 AM Baptiste Jonglez via cfarm-users > > <cfarm-users@lists.tetaneutral.net> wrote: > > > > > > According to ansible [https://cfarm.tetaneutral.net/machines/list/] gcc112 > > > has 160 cores, and gcc135 has 128 cores. Is ansible getting this wrong? > > > > 8 threads per core. It really does not make sense to target more than > > one job for each core. Things will just get horribly slow. > > No, that's not true, up to 4 jobs per core still gives considerable > speedup (and 8 a little too, depends). Performance _per thread_ is lower > of course, but aggregate is higher. SMT4 gets about twice as much work > done as single-threaded (which means each thread gets about half as much > done, but the total doubles). Very roughly, depends on what you are doing > exactly, etc. > > lscpu gets it right on all these machines btw (110, 112, 135); what does > ansible use?
Ansible parses /proc/cpuinfo: https://github.com/ansible/ansible/blob/devel/lib/ansible/module_utils/facts/hardware/linux.py#L181 Do you know how lscpu gets its information? If somebody comes up with an ansible patch that gets the number of CPU/cores/threads right on most farm machines, we can easily backport it to the live cfarm system (we are already doing this with a patch from Anatoly to properly support SPARC64, for gcc202).
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