path: root/Documentation/cputopology.txt
diff options
authorBen Hutchings <>2008-06-04 21:47:29 -0700
committerIngo Molnar <>2008-06-13 10:09:46 +0200
commitc50cbb05a05cf1f9ca3592272eff053c847727d8 (patch)
treee64a380282a16a9a593c07df8d50b729c825ccc0 /Documentation/cputopology.txt
parentaab2545fdd6641b76af0ae96456c4ca9d1e50dad (diff)
cpu topology: always define CPU topology information
This can result in an empty topology directory in sysfs, and requires in-kernel users to protect all uses with #ifdef - see <>. The documentation of CPU topology specifies what the defaults should be if only partial information is available from the hardware. So we can provide these defaults as a fallback. This patch: - Adds default definitions of the 4 topology macros to <linux/topology.h> - Changes drivers/base/topology.c to use the topology macros unconditionally and to cope with definitions that aren't lvalues - Updates documentation accordingly [ From: Andrew Morton <> - fold now-duplicated code - fix layout ] Signed-off-by: Ben Hutchings <> Cc: Vegard Nossum <> Cc: Nick Piggin <> Cc: Chandra Seetharaman <> Cc: Suresh Siddha <> Cc: Mike Travis <> Cc: Christoph Lameter <> Cc: John Hawkes <> Cc: Zhang, Yanmin <> Signed-off-by: Andrew Morton <> Signed-off-by: Ingo Molnar <>
Diffstat (limited to 'Documentation/cputopology.txt')
1 files changed, 9 insertions, 17 deletions
diff --git a/Documentation/cputopology.txt b/Documentation/cputopology.txt
index b61cb9564023..bd699da24666 100644
--- a/Documentation/cputopology.txt
+++ b/Documentation/cputopology.txt
@@ -14,9 +14,8 @@ represent the thread siblings to cpu X in the same physical package;
To implement it in an architecture-neutral way, a new source file,
drivers/base/topology.c, is to export the 4 attributes.
-If one architecture wants to support this feature, it just needs to
-implement 4 defines, typically in file include/asm-XXX/topology.h.
-The 4 defines are:
+For an architecture to support this feature, it must define some of
+these macros in include/asm-XXX/topology.h:
#define topology_physical_package_id(cpu)
#define topology_core_id(cpu)
#define topology_thread_siblings(cpu)
@@ -25,17 +24,10 @@ The 4 defines are:
The type of **_id is int.
The type of siblings is cpumask_t.
-To be consistent on all architectures, the 4 attributes should have
-default values if their values are unavailable. Below is the rule.
-1) physical_package_id: If cpu has no physical package id, -1 is the
-default value.
-2) core_id: If cpu doesn't support multi-core, its core id is 0.
-3) thread_siblings: Just include itself, if the cpu doesn't support
-4) core_siblings: Just include itself, if the cpu doesn't support
-multi-core and HT/Multi-thread.
-So be careful when declaring the 4 defines in include/asm-XXX/topology.h.
-If an attribute isn't defined on an architecture, it won't be exported.
+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