On 25/01/2021 11:50, Song Bao Hua (Barry Song) wrote: > >> -----Original Message----- >> From: Dietmar Eggemann [mailto:dietmar.eggemann@xxxxxxx] >> Sent: Wednesday, January 13, 2021 12:00 AM >> To: Morten Rasmussen <morten.rasmussen@xxxxxxx>; Tim Chen >> <tim.c.chen@xxxxxxxxxxxxxxx> >> Cc: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx>; >> valentin.schneider@xxxxxxx; catalin.marinas@xxxxxxx; will@xxxxxxxxxx; >> rjw@xxxxxxxxxxxxx; vincent.guittot@xxxxxxxxxx; lenb@xxxxxxxxxx; >> gregkh@xxxxxxxxxxxxxxxxxxx; Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>; >> mingo@xxxxxxxxxx; peterz@xxxxxxxxxxxxx; juri.lelli@xxxxxxxxxx; >> rostedt@xxxxxxxxxxx; bsegall@xxxxxxxxxx; mgorman@xxxxxxx; >> mark.rutland@xxxxxxx; sudeep.holla@xxxxxxx; aubrey.li@xxxxxxxxxxxxxxx; >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; >> linux-acpi@xxxxxxxxxxxxxxx; linuxarm@xxxxxxxxxxxxx; xuwei (O) >> <xuwei5@xxxxxxxxxx>; Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>; tiantao (H) >> <tiantao6@xxxxxxxxxxxxx> >> Subject: Re: [RFC PATCH v3 0/2] scheduler: expose the topology of clusters and >> add cluster scheduler >> >> On 11/01/2021 10:28, Morten Rasmussen wrote: >>> On Fri, Jan 08, 2021 at 12:22:41PM -0800, Tim Chen wrote: >>>> >>>> >>>> On 1/8/21 7:12 AM, Morten Rasmussen wrote: >>>>> On Thu, Jan 07, 2021 at 03:16:47PM -0800, Tim Chen wrote: >>>>>> On 1/6/21 12:30 AM, Barry Song wrote: [...] >> wake_wide() switches between packing (select_idle_sibling(), llc_size >> CPUs) and spreading (find_idlest_cpu(), all CPUs). >> >> AFAICS, since none of the sched domains set SD_BALANCE_WAKE, currently >> all wakeups are (llc-)packed. > > Sorry for late response. I was struggling with some other topology > issues recently. > > For "all wakeups are (llc-)packed", > it seems you mean current want_affine is only affecting the new_cpu, > and for wake-up path, we will always go to select_idle_sibling() rather > than find_idlest_cpu() since nobody sets SD_WAKE_BALANCE in any > sched_domain ? > >> >> select_task_rq_fair() >> >> for_each_domain(cpu, tmp) >> >> if (tmp->flags & sd_flag) >> sd = tmp; >> >> >> In case we would like to further distinguish between llc-packing and >> even narrower (cluster or MC-L2)-packing, we would introduce a 2. level >> packing vs. spreading heuristic further down in sis(). > > I didn't get your point on "2 level packing". Would you like > to describe more? It seems you mean we need to have separate > calculation for avg_scan_cost and sched_feat(SIS_) for cluster > (or MC-L2) since cluster and llc are not in the same level > physically? By '1. level packing' I meant going sis() (i.e. sd=per_cpu(sd_llc, target)) instead of routing WF_TTWU through find_idlest_cpu() which uses a broader sd span (in case all sd's (or at least up to an sd > llc) would have SD_BALANCE_WAKE set). wake_wide() (wakee/waker flip heuristic) is currently used to make this decision. But since no sd sets SD_BALANCE_WAKE we always go sis() for WF_TTWU. '2. level packing' would be the decision between cluster- and llc-packing. The question was which heuristic could be used here. >> IMHO, Barry's current implementation doesn't do this right now. Instead >> he's trying to pack on cluster first and if not successful look further >> among the remaining llc CPUs for an idle CPU. > > Yes. That is exactly what the current patch is doing. And this will be favoring cluster- over llc-packing for each task instead.
