Messages in this thread | | | Date | Mon, 14 Mar 2022 18:10:58 +0000 | From | Ionela Voinescu <> | Subject | Re: [PATCH v1 0/3] arch_topology: Correct CPU capacity scaling |
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Hi Leo,
On Sunday 13 Mar 2022 at 13:55:09 (+0800), Leo Yan wrote: > This patch set is to address issues for CPU capacity scaling. > > "capacity-dmips-mhz" property might be absent in all CPU nodes, and in > another situation, DT might have inconsistent binding issue, e.g. some > CPU nodes have "capacity-dmips-mhz" property and some nodes miss the > property. Current code mixes these two cases and always rollback to CPU > capacity 1024 for these two cases. > > Patches 01 and 02 in this set are used to distinguish the two different > DT binding cases, and for the inconsistent binding issue, it rolls back > to 1024 without CPU capacity scaling. > > Patch 03 is to handle the case for absenting "capacity-dmips-mhz" > property in CPU nodes, the patch proceeds to do CPU capacity scaling based > on CPU maximum capacity. Thus it can reflect the correct CPU capacity for > Arm platforms with "fast" and "slow" clusters (CPUs in two clusters have > the same raw capacity but with different maximum frequencies). >
In my opinion it's difficult to handle absent "capacity-dmips-mhz" properties, as they can be a result of 3 scenarios: potential.. 1. bug in DT 2. unwillingness to fill this information in DT 3. suggestion that we're dealing with CPUs with same u-arch (same capacity-dmips-mhz)
I'm not sure it's up to us to interpret suggestions in the code so I believe treating missing information as error is the right choice, which is how we're handling this now.
For 3. (and patch 03), isn't it easier to populate capacity-dmips-mhz to the same value (say 1024) in DT? That is a clear message that we're dealing with CPUs with the same u-arch.
Thanks, Ionela.
> This patch set is applied on the mainline kernel with the latest commit > 68453767131a ("ARM: Spectre-BHB: provide empty stub for non-config"). > And tested on Arm64 Hikey960 platform (with a bit hacking to emulate > fast and slow clusters). > > > Leo Yan (3): > arch_topology: Correct semantics for 'cap_parsing_failed' > arch_topology: Handle inconsistent binding of CPU raw capacity > arch_topology: Scale CPU capacity if without CPU raw capacity > > drivers/base/arch_topology.c | 42 +++++++++++++++++++++++++++++------- > 1 file changed, 34 insertions(+), 8 deletions(-) > > -- > 2.25.1 > >
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