Messages in this thread | | | Date | Wed, 5 Sep 2018 04:14:36 -0700 | From | Srikar Dronamraju <> | Subject | Re: [RFC PATCH 3/4] sched/topology: remove smt_gain |
| |
* Vincent Guittot <vincent.guittot@linaro.org> [2018-09-05 11:11:35]:
> On Wed, 5 Sep 2018 at 10:50, Srikar Dronamraju > <srikar@linux.vnet.ibm.com> wrote: > > > > * Vincent Guittot <vincent.guittot@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.
-- Thanks and Regards Srikar Dronamraju
| |