Messages in this thread | | | Date | Thu, 7 Jul 2022 15:44:04 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH 5/8] arm64: Create cache sysfs directory without ACPI PPTT for hardware prefetch control |
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On Thu, Jul 07, 2022 at 09:37:57AM -0500, Jeremy Linton wrote: > Hi, > > On 2/1/22 05:56, tarumizu.kohei@fujitsu.com wrote: > > > I am assuming this is ACPI enabled system. > > > > Yes, it is ACPI enabled system. > > > > > This looks bit hacky in my opinion. Before I explore better way of adding it, I would > > > like to check if you have explored ways to add PPTT reading these registers from > > > UEFI/EDK2 as PPTT has other topology information which you will need anyways. > > > That would simplify handling of these cacheinfo sysfs in the kernel. Let me know > > > what are your thoughts ? > > > > The latest firmware of ARM64 machine, FX700 with the A64FX processor > > does not support PPTT. > > I think adding PPTT is the best way to generate cacheinfo sysfs. > > However, it is difficult to modify the firmware to add PPTT, so > > it is not clear when it will be possible. > > Therefore, I would like to implement the function in the kernel on > > the condition that firmware does not support PPTT. > > As a bit of a late comment here, I assume you tried injecting the PPTT via > the initrd (directions in admin-guide/acpi/initrd_table_override.txt) then? > That is one of the usual kernel workarounds for broken/missing ACPI tables. > > As mentioned above, besides not providing appropriate topology information > to userspace, not having the PPTT is also possibly causing suboptimal > scheduling decisions in the kernel itself. >
Thanks a lot for the suggestion Jeremy. For some reason, I missed to follow up on this after my initial response. Anyways I agree injecting PPTT via initrd is a good compromise on systems that are shipped without or broken PPTT. I have tested that to be fully functional on v5.19-rc* on one of the servers shipped with broken PPTT.
-- Regards, Sudeep
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