[PATCH v2 2/9] Documentation: update cputopology.txt

Bartosz Golaszewski
2015-05-04T10:29:53Z

The documentation on cpu topology seems to be a bit out-of-date. It
doesn't mention the **_siblings_list attributes and uses old names
for topology_**_cpumask() macros.

Add information on missing attributes plus some additional
clarifications.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
---
Documentation/cputopology.txt | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/Documentation/cputopology.txt b/Documentation/cputopology.txt
index 428a961..12b1b25 100644
--- a/Documentation/cputopology.txt
+++ b/Documentation/cputopology.txt
@@ -1,6 +1,6 @@

Export CPU topology info via sysfs. Items (attributes) are similar
-to /proc/cpuinfo.
+to /proc/cpuinfo output of some architectures:

1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:

@@ -23,20 +23,35 @@ to /proc/cpuinfo.
4) /sys/devices/system/cpu/cpuX/topology/thread_siblings:

internal kernel map of cpuX's hardware threads within the same
- core as cpuX
+ core as cpuX.

-5) /sys/devices/system/cpu/cpuX/topology/core_siblings:
+5) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list:
+
+ human-readable list of cpuX's hardware threads within the same
+ core as cpuX.
+
+6) /sys/devices/system/cpu/cpuX/topology/core_siblings:

internal kernel map of cpuX's hardware threads within the same
physical_package_id.

-6) /sys/devices/system/cpu/cpuX/topology/book_siblings:
+7) /sys/devices/system/cpu/cpuX/topology/core_siblings_list:
+
+ human-readable list of cpuX's hardware threads within the same
+ physical_package_id.
+
+8) /sys/devices/system/cpu/cpuX/topology/book_siblings:

internal kernel map of cpuX's hardware threads within the same
book_id.

+9) /sys/devices/system/cpu/cpuX/topology/book_siblings_list:
+
+ human-readable list of cpuX's hardware threads within the same
+ book_id.
+
To implement it in an architecture-neutral way, a new source file,
-drivers/base/topology.c, is to export the 4 or 6 attributes. The two book
+drivers/base/topology.c, is to export the 6 or 9 attributes. The three book
related sysfs files will only be created if CONFIG_SCHED_BOOK is selected.

For an architecture to support this feature, it must define some of
@@ -48,16 +63,18 @@ these macros in include/asm-XXX/topology.h:
#define topology_core_cpumask(cpu)
#define topology_book_cpumask(cpu)

-The type of **_id is int.
-The type of siblings is (const) struct cpumask *.
+The type of **_id macros is int.
+The type of **_cpumask macros is (const) struct cpumask *. The latter
+correspond with appropriate **_siblings sysfs attributes (except for
+topology_sibling_cpumask() which corresponds with thread_siblings).

To be consistent on all architectures, include/linux/topology.h
provides default definitions for any of the above macros that are
not defined by include/asm-XXX/topology.h:
1) physical_package_id: -1
2) core_id: 0
-3) thread_siblings: just the given CPU
-4) core_siblings: just the given CPU
+3) sibling_cpumask: just the given CPU
+4) core_cpumask: just the given CPU

For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
default definitions for topology_book_id() and topology_book_cpumask().
--
2.1.4