Messages in this thread | | | Date | Mon, 13 Jun 2022 11:19:36 +0200 | From | Dietmar Eggemann <> | Subject | Re: [PATCH v3 15/16] arch_topology: Set cluster identifier in each core/thread from /cpu-map |
| |
On 10/06/2022 12:27, Sudeep Holla wrote: > On Fri, Jun 10, 2022 at 12:08:44PM +0200, Vincent Guittot wrote: >> On Mon, 6 Jun 2022 at 12:22, Sudeep Holla <sudeep.holla@arm.com> wrote: >>> > > [...] > >>> Why ? Are you suggesting that we shouldn't present the hardware cluster >>> to the topology because of the above reason ? If so, sorry that is not a >>> valid reason. We could add login to return NULL or appropriate value >>> needed in cpu_clustergroup_mask id it matches MC level mask if we can't >>> deal that in generic scheduler code. But the topology code can't be >>> compromised for that reason as it is user visible. >> >> I tend to agree with Dietmar. The legacy use of cluster node in DT >> refers to the dynamiQ or legacy b.L cluster which is also aligned to >> the LLC and the MC scheduling level. The new cluster level that has >> been introduced recently does not target this level but some >> intermediate levels either inside like for the kupeng920 or the v9 >> complex or outside like for the ampere altra. So I would say that >> there is one cluster node level in DT that refers to the same MC/LLC >> level and only an additional child/parent cluster node should be used >> to fill the clustergroup_mask. >> > > Again I completely disagree. Let us look at the problems separately. > The hardware topology that some of the tools like lscpu and lstopo expects > what the hardware looks like and not the scheduler's view of the hardware. > So the topology masks that gets exposed to the user-space needs fixing > even today. I have reports from various tooling people about the same. > E.g. Juno getting exposed as dual socket system is utter non-sense. > > Yes scheduler uses most of the topology masks as is but that is not a must. > There are these *group_mask functions that can implement what scheduler > needs to be fed. > > I am not sure why the 2 issues are getting mixed up and that is the main > reason why I jumped into this to make sure the topology masks are > not tampered based on the way it needs to be used for scheduler.
I'm all in favor of not mixing up those 2 issues. But I don't understand why you have to glue them together.
(1) DT systems broken in userspace (lstopo shows Juno with 2 Packages)
(2) Introduce CONFIG_SCHED_CLUSTER for DT systems
(1) This can be solved with your patch-set w/o setting `(1. level) cpu-map cluster nodes`. The `socket nodes` taking over the functionality of the `cluster nodes` sorts out the `Juno is seen as having 2 packages`. This will make core_sibling not suitable for cpu_coregroup_mask() anymore. But this is OK since llc from cacheinfo (i.e. llc_sibling) takes over here. There is no need to involve `cluster nodes` anymore.
(2) This will only make sense for Armv9 L2 complexes if we connect `2. level cpu-map cluster nodes` with cluster_id and cluster_sibling. And only then clusters would mean the same thing in ACPI and DT. I guess this was mentioned already a couple of times.
> Both ACPI and DT on a platform must present exact same hardware topology > to the user-space, there is no space for argument there. > >> IIUC, we don't describe the dynamiQ level in ACPI which uses cache >> topology instead to define cpu_coregroup_mask whereas DT described the >> dynamiQ instead of using cache topology. If you use cache topology >> now, then you should skip the dynamiQ >> > > Yes, unless someone can work out a binding to represent that and convince > DT maintainers ;). > >> Finally, even if CLS and MC have the same scheduling behavior for now, >> they might ends up with different scheduling properties which would >> mean that replacing MC level by CLS one for current SoC would become >> wrong >> > > Again as I mentioned to Dietmar, that is something we can and must deal with > in those *group_mask and not expect topology mask to be altered to meet > CLS/MC or whatever sched domains needs. Sorry, that is my strong opinion > as the topology is already user-space visible and (tooling) people are > complaining that DT systems are broken and doesn't match ACPI systems. > > So unless someone gives me non-scheduler and topology specific reasons > to change that, sorry but my opinion on this matter is not going to change ;).
`lstopo` is fine with a now correct /sys/.../topology/package_cpus (or core_siblings (old filename). It's not reading /sys/.../topology/cluster_cpus (yet) so why set it (wrongly) to 0x39 for CPU0 on Juno when it can stay 0x01?
> You will get this view of topology, find a way to manage with all those > *group_mask functions. By the way it is already handled for ACPI systems, > so if you are not happy with that, then that needs fixing as this change > set just aligns the behaviour on similar ACPI system. So the Juno example > is incorrect for the reason that the behaviour of scheduler there is different > with DT and ACPI.
[...]
| |