percpu: align percpu readmostly subsection to cacheline

Currently percpu readmostly subsection may share cachelines with other
percpu subsections which may result in unnecessary cacheline bounce
and performance degradation.

This patch adds @cacheline parameter to PERCPU() and PERCPU_VADDR()
linker macros, makes each arch linker scripts specify its cacheline
size and use it to align percpu subsections.

This is based on Shaohua's x86 only patch.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Shaohua Li <shaohua.li@intel.com>

1 files changed, 22 insertions, 13 deletions

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6ebb81030d2d..439df587c12c 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -15,7 +15,7 @@
  *      HEAD_TEXT_SECTION
  *      INIT_TEXT_SECTION(PAGE_SIZE)
  *      INIT_DATA_SECTION(...)
- *      PERCPU(PAGE_SIZE)
+ *      PERCPU(CACHELINE_SIZE, PAGE_SIZE)
  *      __init_end = .;
  *
  *      _stext = .;
@@ -683,13 +683,18 @@
 
 /**
  * PERCPU_VADDR - define output section for percpu area
+ * @cacheline: cacheline size
  * @vaddr: explicit base address (optional)
  * @phdr: destination PHDR (optional)
  *
- * Macro which expands to output section for percpu area.  If @vaddr
- * is not blank, it specifies explicit base address and all percpu
- * symbols will be offset from the given address.  If blank, @vaddr
- * always equals @laddr + LOAD_OFFSET.
+ * Macro which expands to output section for percpu area.
+ *
+ * @cacheline is used to align subsections to avoid false cacheline
+ * sharing between subsections for different purposes.
+ *
+ * If @vaddr is not blank, it specifies explicit base address and all
+ * percpu symbols will be offset from the given address.  If blank,
+ * @vaddr always equals @laddr + LOAD_OFFSET.
  *
  * @phdr defines the output PHDR to use if not blank.  Be warned that
  * output PHDR is sticky.  If @phdr is specified, the next output
@@ -700,7 +705,7 @@
  * If there is no need to put the percpu section at a predetermined
  * address, use PERCPU().
  */
-#define PERCPU_VADDR(vaddr, phdr)                                       \
+#define PERCPU_VADDR(cacheline, vaddr, phdr)                            \
         VMLINUX_SYMBOL(__per_cpu_load) = .;                             \
         .data..percpu vaddr : AT(VMLINUX_SYMBOL(__per_cpu_load)         \
                                 - LOAD_OFFSET) {                        \
@@ -708,7 +713,9 @@
                 *(.data..percpu..first)                                 \
                 . = ALIGN(PAGE_SIZE);                                   \
                 *(.data..percpu..page_aligned)                          \
+                . = ALIGN(cacheline);                                   \
                 *(.data..percpu..readmostly)                            \
+                . = ALIGN(cacheline);                                   \
                 *(.data..percpu)                                        \
                 *(.data..percpu..shared_aligned)                        \
                 VMLINUX_SYMBOL(__per_cpu_end) = .;                      \
@@ -717,18 +724,18 @@
 
 /**
  * PERCPU - define output section for percpu area, simple version
+ * @cacheline: cacheline size
  * @align: required alignment
  *
- * Align to @align and outputs output section for percpu area.  This
- * macro doesn't maniuplate @vaddr or @phdr and __per_cpu_load and
+ * Align to @align and outputs output section for percpu area.  This macro
+ * doesn't manipulate @vaddr or @phdr and __per_cpu_load and
  * __per_cpu_start will be identical.
  *
- * This macro is equivalent to ALIGN(align); PERCPU_VADDR( , ) except
- * that __per_cpu_load is defined as a relative symbol against
- * .data..percpu which is required for relocatable x86_32
- * configuration.
+ * This macro is equivalent to ALIGN(@align); PERCPU_VADDR(@cacheline,,)
+ * except that __per_cpu_load is defined as a relative symbol against
+ * .data..percpu which is required for relocatable x86_32 configuration.
  */
-#define PERCPU(align)                                                   \
+#define PERCPU(cacheline, align)                                        \
         . = ALIGN(align);                                               \
         .data..percpu   : AT(ADDR(.data..percpu) - LOAD_OFFSET) {       \
                 VMLINUX_SYMBOL(__per_cpu_load) = .;                     \
@@ -736,7 +743,9 @@
                 *(.data..percpu..first)                                 \
                 . = ALIGN(PAGE_SIZE);                                   \
                 *(.data..percpu..page_aligned)                          \
+                . = ALIGN(cacheline);                                   \
                 *(.data..percpu..readmostly)                            \
+                . = ALIGN(cacheline);                                   \
                 *(.data..percpu)                                        \
                 *(.data..percpu..shared_aligned)                        \
                 VMLINUX_SYMBOL(__per_cpu_end) = .;                      \