On 2/13/25 14:51, Juri Lelli wrote: > On 13/02/25 13:38, Christian Loehle wrote: >> On 2/13/25 13:33, Juri Lelli wrote: > > ... > >>> Not sure I get what your worry is, sorry. In my understanding when the >>> last cpu of a policy/cluster gets offlined the corresponding sugov >>> kthread gets stopped as well (sugov_exit)? >>> >> >> The other way round. >> We may have sugov kthread of cluster [6,7] affined to CPU1. Is it >> guaranteed that we cannot offline CPU1 (while CPU6 or CPU7 are still >> online)? > > Uhu, is this a sane/desired setup? Anyway, I would say that if CPU1 is > offlined sugov[6,7] will need to be migrated someplace else. Sane? I guess that's to be discussed. It is definitely desirable unfortunately. As mentioned I experimented with having sugov DL tasks (as they cause a lot of idle wakeups (which are expensive on the bigger CPUs)) both always run locally and never IPI (but that means we have contention and still run a double switch on an 'expensive' CPU) and run that on a little CPU and the latter had much better results. > >> Or without the affinity: >> cluster [6,7] with isolcpu=6 (i.e. sugov kthread of that cluster can >> only run on CPU7). Is offlining of CPU6 then prevented (as long as >> CPU7 is online)? >> I don't see how. >> Anyway we probably want to change isolcpu and affinity to merely be >> a suggestion for the sugov DL case. Fundamentally it belongs to what >> is run on that CPU anyway. > > I would tend to agree. I'll write something up.
