On 2/13/25 13:33, Juri Lelli wrote: > On 13/02/25 12:27, Christian Loehle wrote: >> On 2/13/25 06:20, Juri Lelli wrote: >>> On 12/02/25 19:22, Dietmar Eggemann wrote: >>>> On 11/02/2025 11:42, Juri Lelli wrote: >>> >>> ... >>> >>>>> What about we actually ignore them consistently? We already do that for >>>>> admission control, so maybe we can do that when rebuilding domains as >>>>> well (until we find maybe a better way to deal with them). >>>>> >>>>> Does the following make any difference? >>>> >>>> It at least seems to solve the issue. And like you mentioned on irc, we >>>> don't know the bw req of sugov anyway. >>>> >>>> So with this change we start with 'dl_bw->total_bw = 0' even w/ sugov tasks. >>>> >>>> dl_rq[0]: >>>> .dl_nr_running : 0 >>>> .dl_bw->bw : 996147 >>>> .dl_bw->total_bw : 0 <-- ! >>>> >>>> IMHO, people who want to run serious DL can always check whether there >>>> are already these infrastructural DL tasks or even avoid schedutil. >>> >>> It definitely not ideal and admittedly gross, but not worse than what we >>> are doing already considering we ignore sugovs at AC and the current >>> bandwidth allocation its there only to help with PI. So, duck tape. :/ >>> >>> A more proper way to work with this would entail coming up with sensible >>> bandwidth allocation for sugovs, but that's most probably hardware >>> specific, so I am not sure how we can make that general enough. >>> >>> Anyway, looks like Jon was still seeing the issue. I asked him to verify >>> he is using all the proposed changes. Let's see what he reports. >> >> FWIW it also fixes my reproducer. >> >> I agree that dummy numbers for sugov bw is futile, but real bw numbers >> also don't make a lot of sense (what if we exceed them? The system >> won't be able to change frequency, i.e. might not be able to provide >> bw for other DL tasks then either?). >> I'm slightly worried about now allowing the last legal CPU for a sugov >> cluster to offline, which would lead to a cluster still being active >> but sugov DL unable to run anywhere. I can't reproduce this currently >> though. Is this an issue in theory? Or am I missing something? > > 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)? 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.
