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percpu: align percpu readmostly subsection to cacheline

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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>
This commit is contained in:
Tejun Heo 2011-01-25 14:26:50 +01:00
parent c723fdab8a
commit 19df0c2fef
19 changed files with 41 additions and 32 deletions
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35
include/asm-generic/vmlinux.lds.h
View file

@ -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) = .; \