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@kernel.org wrote:
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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
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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*/.
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