On Wed, 5 Sep 2018 at 13:14, Srikar Dronamraju <sri...@linux.vnet.ibm.com> wrote: > > * Vincent Guittot <vincent.guit...@linaro.org> [2018-09-05 11:11:35]: > > > On Wed, 5 Sep 2018 at 10:50, Srikar Dronamraju > > <sri...@linux.vnet.ibm.com> wrote: > > > > > > * Vincent Guittot <vincent.guit...@linaro.org> [2018-09-05 09:36:42]: > > > > > > > > > > > > > I dont know of any systems that have come with single threaded and > > > > > multithreaded. However some user can still offline few threads in a > > > > > core > > > > > while leaving other cores untouched. I dont really know why somebody > > > > > would want to do it. For example, some customer was toying with SMT 3 > > > > > mode in a SMT 8 power8 box. > > > > > > > > In this case, it means that we have the same core capacity whatever > > > > the number of CPUs > > > > and a core with SMT 3 will be set with the same compute capacity as > > > > the core with SMT 8. > > > > Does it still make sense ? > > > > > > > > > > To me it make sense atleast from a power 8 perspective, because SMT 1 > > > > SMT 2 > SMT 4 > SMT8. So if one core is configured for SMT 2 and other > > > core is configured for SMT4; all threads being busy, the individual > > > threads running on SMT2 core will complete more work than SMT 4 core > > > threads. > > > > I agree for individual thread capacity but at core group level, the > > core SMT 1 will have the same capacity as core group SMT 8 so load > > balance will try to balance evenly the tasks between the 2 cores > > whereas core SMT 8 > core SMT1 , isn't it ? > > > > I believe that Core capacity irrespective of the number of threads > should be similar. We wanted to give a small benefit if the core has > multiple threads and that was smt_gain. Lets say we have 8 equal sw > threads running on 2 cores; one being SMT 2 and other being SMT4. > then 4 threads should be spread to each core. So that we would be fair > to each of the 8 SW threads.
Do you mean that it would be the same with SMT 2 and SMT 8 ? evenly spread the 8 SW threads between the 2 cores would be better than 2 SW threads on core SMT 2 and 6 on core SMT8 > > -- > Thanks and Regards > Srikar Dronamraju >
