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Message-ID: <57719c05-6470-40c8-8ecf-daa4ad1006da@arm.com>
Date: Tue, 14 Oct 2025 17:54:14 -0500
From: Jeremy Linton <jeremy.linton@....com>
To: Feng Tang <feng.tang@...ux.alibaba.com>,
"Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Sudeep Holla <sudeep.holla@....com>, James Morse <james.morse@....com>
Subject: Re: [PATCH] ACPI: PPTT: Dump PPTT table when error detected
Hi,
On 10/14/25 3:51 AM, 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 when there
> is warning about it.
>
> The dumped info 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
This is an interesting idea, particularly if the dump is smarter and
acts like a linter, but i'm not sure the output right now would have
helped with the original problem. In that respect simply sprinkling a
lot of pr_debug information around during the parsing might be more
helpful to understand the context around parse errors.
I was under the impression doing that was frowned on, as I ended up
removing quite a number of them during the initial reviews.
I wonder if simply print_hex_dump'ing the table on certain errors with
some acpi=debug like option is just as useful. Particularly if someone
writes a better userspace pptt pretty printer, since the iasl output
isn't helpful to understand the tree relationships.
> ...
>
> From it, we can see the processor/cache info and the hierarchy relation
> between them.
>
> Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>
> ---
> drivers/acpi/pptt.c | 75 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 75 insertions(+)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 54676e3d82dd..e7b48a77a12f 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -498,6 +498,79 @@ static void acpi_pptt_warn_missing(void)
> pr_warn_once("No PPTT table found, CPU and cache topology may be inaccurate\n");
> }
>
> +static void acpi_dump_pptt_table(struct acpi_table_header *table_hdr)
> +{
> + struct acpi_subtable_header *entry, *entry_start;
> + unsigned long end;
> + struct acpi_pptt_processor *cpu;
> + struct acpi_pptt_cache *cache;
> + u32 entry_sz, i;
> + u8 len;
> + static bool dumped;
> +
> + /* PPTT table could be pretty big, no need to dump it twice */
> + if (dumped)
> + return;
> + dumped = true;
> +
> + end = (unsigned long)table_hdr + table_hdr->length;
> + entry_start = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr,
> + sizeof(struct acpi_table_pptt));
> +
> + pr_info("Processors:\n");
> + entry_sz = sizeof(struct acpi_pptt_processor);
> + entry = entry_start;
> + i = 0;
> + while ((unsigned long)entry + entry_sz <= end) {
> + len = entry->length;
> + if (!len) {
> + pr_warn("Invalid zero length subtable\n");
> + return;
> + }
> +
> + cpu = (struct acpi_pptt_processor *)entry;
> + entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry, len);
> +
> + if (cpu->header.type != ACPI_PPTT_TYPE_PROCESSOR)
> + continue;
> +
> + printk(KERN_INFO "P[%3d][0x%04lx]: parent=0x%04x acpi_proc_id=%3d num_res=%d flags=0x%02x(%s%s%s)\n",
> + i++, (unsigned long)cpu - (unsigned long)table_hdr,
> + cpu->parent, cpu->acpi_processor_id,
> + cpu->number_of_priv_resources, cpu->flags,
> + cpu->flags & ACPI_PPTT_PHYSICAL_PACKAGE ? "package" : "",
> + cpu->flags & ACPI_PPTT_ACPI_LEAF_NODE ? "leaf" : "",
> + cpu->flags & ACPI_PPTT_ACPI_PROCESSOR_IS_THREAD ? ", thread" : ""
> + );
> +
> + }
> +
> + pr_info("Caches:\n");
> + entry_sz = sizeof(struct acpi_pptt_cache);
> + entry = entry_start;
> + i = 0;
> + while ((unsigned long)entry + entry_sz <= end) {
> + len = entry->length;
> + if (!len) {
> + pr_warn("Invalid zero length subtable\n");
> + return;
> + }
> +
> + cache = (struct acpi_pptt_cache *)entry;
> + entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry, len);
> +
> + if (cache->header.type != ACPI_PPTT_TYPE_CACHE)
> + continue;
> +
> + printk(KERN_INFO "C[%4d][0x%04lx]: flags=0x%02x next_level=0x%04x size=0x%-8x sets=%-6d way=%-2d attribute=0x%-2x line_size=%d\n",
> + i++, (unsigned long)cache - (unsigned long)table_hdr,
> + cache->flags, cache->next_level_of_cache, cache->size,
> + cache->number_of_sets, cache->associativity,
> + cache->attributes, cache->line_size
> + );
> + }
> +}
> +
> /**
> * topology_get_acpi_cpu_tag() - Find a unique topology value for a feature
> * @table: Pointer to the head of the PPTT table
> @@ -534,6 +607,8 @@ static int topology_get_acpi_cpu_tag(struct acpi_table_header *table,
> }
> pr_warn_once("PPTT table found, but unable to locate core %d (%d)\n",
> cpu, acpi_cpu_id);
> +
> + acpi_dump_pptt_table(table);
> return -ENOENT;
> }
>
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