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Date: Fri, 20 May 2022 16:33:09 +0100 From: Sudeep Holla <sudeep.holla@....com> To: Ionela Voinescu <ionela.voinescu@....com> Cc: Atish Patra <atishp@...shpatra.org>, linux-kernel@...r.kernel.org, Atish Patra <atishp@...osinc.com>, Vincent Guittot <vincent.guittot@...aro.org>, Sudeep Holla <sudeep.holla@....com>, Morten Rasmussen <morten.rasmussen@....com>, Dietmar Eggemann <dietmar.eggemann@....com>, Qing Wang <wangqing@...o.com>, linux-arm-kernel@...ts.infradead.org, linux-riscv@...ts.infradead.org, Rob Herring <robh+dt@...nel.org> Subject: Re: [PATCH v2 0/8] arch_topology: Updates to add socket support and fix cluster ids On Thu, May 19, 2022 at 05:32:49PM +0100, Ionela Voinescu wrote: > Hi Sudeep, > > On Wednesday 18 May 2022 at 10:33:17 (+0100), Sudeep Holla wrote: > > Hi All, > > > > This series intends to fix some discrepancies we have in the CPU topology > > parsing from the device tree /cpu-map node. Also this diverges from the > > behaviour on a ACPI enabled platform. The expectation is that both DT > > and ACPI enabled systems must present consistent view of the CPU topology. > > > > Currently we assign generated cluster count as the physical package identifier > > for each CPU which is wrong. The device tree bindings for CPU topology supports > > sockets to infer the socket or physical package identifier for a given CPU. > > Also we don't check if all the cores/threads belong to the same cluster before > > updating their sibling masks which is fine as we don't set the cluster id yet. > > > > These changes also assigns the cluster identifier as parsed from the device tree > > cluster nodes within /cpu-map without support for nesting of the clusters. > > Finally, it also add support for socket nodes in /cpu-map. With this the > > parsing of exact same information from ACPI PPTT and /cpu-map DT node > > aligns well. > > > > The only exception is that the last level cache id information can be > > inferred from the same ACPI PPTT while we need to parse CPU cache nodes > > in the device tree. > > > > P.S: I have not cc-ed Greg and Rafael so that all the users of arch_topology > > agree with the changes first before we include them. > > > > v1[1]->v2: > > - Updated ID validity check include all non-negative value > > - Added support to get the device node for the CPU's last level cache > > - Added support to build llc_sibling on DT platforms > > > > [1] https://lore.kernel.org/lkml/20220513095559.1034633-1-sudeep.holla@arm.com > > > > Sudeep Holla (8): > > arch_topology: Don't set cluster identifier as physical package identifier > > arch_topology: Set thread sibling cpumask only within the cluster > > arch_topology: Set cluster identifier in each core/thread from /cpu-map > > arch_topology: Add support for parsing sockets in /cpu-map > > arch_topology: Check for non-negative value rather than -1 for IDs validity > > arch_topology: Avoid parsing through all the CPUs once a outlier CPU is found > > of: base: add support to get the device node for the CPU's last level cache > > arch_topology: Add support to build llc_sibling on DT platforms > > > > Just a recommendation for patch-set structure: it would be best to have > the following sequence to maintain the same scheduler topology and > behaviour when partially applying the set (currently testing this on Juno, > but should be the case for other platforms as well): > > 2/8 arch_topology: Set thread sibling cpumask only within the cluster > 5/8 arch_topology: Check for non-negative value rather than -1 for IDs validity > 6/8 arch_topology: Avoid parsing through all the CPUs once a outlier CPU is found > > --> these are only preparation/cleanup patches and don't affect current > functionality > Agreed. It was in my TODO list but I just to post this v2 for some reason. I knew the patches were more in the order of my thoughts on what all needs to be done and the order I added them. I knew it would result in issue with kernel bisection. > 7/8 of: base: add support to get the device node for the CPU's last level cache > 8/8 arch_topology: Add support to build llc_sibling on DT platforms > > --> these will populate llc siblings but this list will be equal to > core siblings (based on package_id) so nothing changes in the scheduler > topology. Even if CONFIG_SCHED_CLUSTER=y, we still have cluster_id=-1 so > nothing will change in that case either, for the patches so far. > Correct, I had worked out this much detail. > 1/8 arch_topology: Don't set cluster identifier as physical package identifier > > --> 1/8 is the trouble maker if it's the first patch as it will result > in having all CPUs in core_siblings so the topology will be flattened to > just an MC level for a typical b.L system like Juno. But if you add it after > all of the above patches, the llc_siblings will contribute to create the same > MC and DIE levels we expect. > > 3/8 arch_topology: Set cluster identifier in each core/thread from /cpu-map > 4/8 arch_topology: Add support for parsing sockets in /cpu-map > > --> Here 3/8 will start creating complications when having clusters in > DT and we have CONFIG_SCHED_CLUSTER=y. But I'll detail this in a reply > to that patch. For CONFIG_SCHED_CLUSTER=n the topology and scheduler > behaviour should be the same as before this set. > Thanks for the ordering of the last 3. I wanted to work out, but you need to have done more work than me on that and thanks for saving my time. Much appreciated. > Hope it helps, Yes definitely, thanks again. -- Regards, Sudeep
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