On 08/03/2022 18:49, Darren Hart wrote: > On Tue, Mar 08, 2022 at 05:03:07PM +0100, Dietmar Eggemann wrote: >> On 08/03/2022 12:04, Vincent Guittot wrote: >>> On Tue, 8 Mar 2022 at 11:30, Will Deacon <will@xxxxxxxxxx> wrote: [...] >> IMHO, if core_mask weight is 1, MC will be removed/degenerated anyway. >> >> This is what I get on my Ampere Altra (I guess I don't have the ACPI >> changes which would let to a CLS sched domain): >> >> # cat /sys/kernel/debug/sched/domains/cpu0/domain*/name >> DIE >> NUMA >> root@oss-altra01:~# zcat /proc/config.gz | grep SCHED_CLUSTER >> CONFIG_SCHED_CLUSTER=y > > I'd like to follow up on this. Would you share your dmidecode BIOS > Information section? # dmidecode -t 0 # dmidecode 3.2 Getting SMBIOS data from sysfs. SMBIOS 3.2.0 present. Handle 0x0000, DMI type 0, 26 bytes BIOS Information Vendor: Ampere(TM) Version: 0.9.20200724 Release Date: 2020/07/24 ROM Size: 7680 kB Characteristics: PCI is supported BIOS is upgradeable Boot from CD is supported Selectable boot is supported ACPI is supported UEFI is supported BIOS Revision: 5.15 Firmware Revision: 0.6 > Which kernel version? v5.17-rc5 [...] >>> I would not say that I'm happy because this solution skews the core >>> cpu mask in order to abuse the scheduler so that it will remove a >>> wrong but useless level when it will build its domains. >>> But this works so as long as the maintainer are happy, I'm fine > > I did explore the other options and they added considerably more > complexity without much benefit in my view. I prefer this option which > maintains the cpu_topology as described by the platform, and maps it > into something that suits the current scheduler abstraction. I agree > there is more work to be done here and intend to continue with it. > >> I do not have any better idea than this tweak here either in case the >> platform can't provide a cleaner setup. > > I'd argue The platform is describing itself accurately in ACPI PPTT > terms. The topology doesn't fit nicely within the kernel abstractions > today. This is an area where I hope to continue to improve things going > forward. I see. And I assume lying about SCU/LLC boundaries in ACPI is not an option since it messes up /sys/devices/system/cpu/cpu0/cache/index*/. [...]
