在 03/07/2019 17:24, Rafael J. Wysocki 写道:

On Fri, Jun 28, 2019 at 8:15 PM Jeremy Linton [off-list ref] wrote:

quoted

ACPI 6.3 adds a flag to the CPU node to indicate whether
the given PE is a thread. Add a function to return that
information for a given linux logical CPU.

Signed-off-by: Jeremy Linton <redacted>
---
  drivers/acpi/pptt.c  | 62 +++++++++++++++++++++++++++++++++++++++++++-
  include/linux/acpi.h |  5 ++++
  2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index b72e6afaa8fb..bb6196422fad 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c

@@ -517,6 +517,52 @@ static int find_acpi_cpu_topology_tag(unsigned int cpu, int level, int flag)
         return retval;
  }

+/**
+ * check_acpi_cpu_flag() - Determine if CPU node has a flag set
+ * @cpu: Kernel logical CPU number
+ * @rev: The PPTT revision defining the flag
+ * @flag: The flag itself
+ *
+ * Check the node representing a CPU for a given flag.
+ *
+ * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be found or
+ *        the table revision isn't new enough.
+ *        1, any passed flag set
+ *        0, flag unset
+ */
+static int check_acpi_cpu_flag(unsigned int cpu, int rev, u32 flag)

Why not bool?

quoted

+{
+       struct acpi_table_header *table;
+       acpi_status status;
+       u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
+       struct acpi_pptt_processor *cpu_node = NULL;
+       int ret = -ENOENT;
+       static int saved_pptt_rev = -1;
+
+       /* Cache the PPTT revision to avoid repeat table get/put on failure */

This is a rather questionable optimization.

Does the extra table get/put really matter?

I would have made saved_pptt_rev a global, but, indeed, caching the 
value is not so important.

quoted

+       if (saved_pptt_rev > -1 && saved_pptt_rev < rev)
+               return -ENOENT;

It should be fine to return 'false' here, shouldn't it?

quoted

+
+       status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
+       if (ACPI_FAILURE(status)) {
+               saved_pptt_rev = 0;
+               acpi_pptt_warn_missing();
+               return ret;

And here?

quoted

+       }
+
+       saved_pptt_rev = table->revision;
+
+       if (saved_pptt_rev >= rev)
+               cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
+
+       if (cpu_node)
+               ret = (cpu_node->flags & flag) != 0;

And this can be

ret = !!(cpu_node->flags & flag);

quoted

+
+       acpi_put_table(table);
+
+       return ret;
+}
+
  /**
   * acpi_find_last_cache_level() - Determines the number of cache levels for a PE
   * @cpu: Kernel logical CPU number

@@ -581,6 +627,21 @@ int cache_setup_acpi(unsigned int cpu)
         return status;
  }

+/**
+ * acpi_pptt_cpu_is_thread() - Determine if CPU is a thread
+ * @cpu: Kernel logical CPU number
+ *
+ *
+ * Return: 1, a thread
+ *         0, not a thread
+ *         -ENOENT ,if the PPTT doesn't exist, the CPU cannot be found or
+ *         the table revision isn't new enough.
+ */
+int acpi_pptt_cpu_is_thread(unsigned int cpu)
+{
+       return check_acpi_cpu_flag(cpu, 2, ACPI_PPTT_ACPI_PROCESSOR_IS_THREAD);
+}

You could also consider the following to avoid the tri-state return value:

bool acpi_pptt_cpu_find_threaded(unsigned int cpu, bool *is_threaded)

quoted

+
  /**
   * find_acpi_cpu_topology() - Determine a unique topology value for a given CPU
   * @cpu: Kernel logical CPU number

@@ -641,7 +702,6 @@ int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
         return ret;
  }

-
  /**
   * find_acpi_cpu_topology_package() - Determine a unique CPU package value
   * @cpu: Kernel logical CPU number

diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index d315d86844e4..3e339375e213 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h

@@ -1301,10 +1301,15 @@ static inline int lpit_read_residency_count_address(u64 *address)
  #endif

  #ifdef CONFIG_ACPI_PPTT
+int acpi_pptt_cpu_is_thread(unsigned int cpu);
  int find_acpi_cpu_topology(unsigned int cpu, int level);
  int find_acpi_cpu_topology_package(unsigned int cpu);
  int find_acpi_cpu_cache_topology(unsigned int cpu, int level);
  #else
+static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
+{
+       return -EINVAL;
+}
  static inline int find_acpi_cpu_topology(unsigned int cpu, int level)
  {
         return -EINVAL;
--

2.21.0

.

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