Re: [PATCH v2] ACPI: PPTT: Dump PPTT table when error detected

Sudeep Holla
2026-01-12T17:03:04Z

On Wed, Dec 31, 2025 at 06:49:09PM +0800, Feng Tang wrote:
> There was warning message about PPTT table:
>
> "ACPI PPTT: PPTT table found, but unable to locate core 1 (1)",
>
> and it in turn caused scheduler warnings when building up the system.
> It took a while to root cause the problem be related a broken PPTT
> table which has wrong cache information.
>
> To speedup debugging similar issues, dump the PPTT table, which makes
> the warning more noticeable and helps bug hunting.
>
> The dumped info format on a ARM server is like:
>
> ACPI PPTT: Processors:
> P[ 0][0x0024]: parent=0x0000 acpi_proc_id= 0 num_res=1 flags=0x11(package)
> P[ 1][0x005a]: parent=0x0024 acpi_proc_id= 0 num_res=1 flags=0x12()
> P[ 2][0x008a]: parent=0x005a acpi_proc_id= 0 num_res=3 flags=0x1a(leaf)
> P[ 3][0x00f2]: parent=0x005a acpi_proc_id= 1 num_res=3 flags=0x1a(leaf)
> P[ 4][0x015a]: parent=0x005a acpi_proc_id= 2 num_res=3 flags=0x1a(leaf)
> ...
> ACPI PPTT: Caches:
> C[ 0][0x0072]: flags=0x7f next_level=0x0000 size=0x4000000 sets=65536 way=16 attribute=0xa line_size=64
> C[ 1][0x00aa]: flags=0x7f next_level=0x00da size=0x10000 sets=256 way=4 attribute=0x4 line_size=64
> C[ 2][0x00c2]: flags=0x7f next_level=0x00da size=0x10000 sets=256 way=4 attribute=0x2 line_size=64
> C[ 3][0x00da]: flags=0x7f next_level=0x0000 size=0x100000 sets=2048 way=8 attribute=0xa line_size=64
> ...
>
> It provides a global and straightforward view of the hierarchy of the
> processor and caches info of the platform, and from the offset info
> (the 3rd column), the child-parent relation could be checked.
>
> With this, the root cause of the original issue was pretty obvious,
> that there were some caches items missing which caused the issue when
> building up scheduler domain.
>

While this may sound like a good idea, it deviates from how errors in other
table-parsing code are handled. Instead of dumping the entire table, it would
be preferable to report the specific issue encountered during parsing.

I do not have a strong objection if Rafael is comfortable with this approach;
however, it does differ from the established pattern used by similar code.
Dumping the entire table in a custom manner is not the standard way of
handling parsing errors. Just my opinion.

--
Regards,
Sudeep