linux-kernel - [patch 2/3] add new macros to make percpu readmostly section correctly align

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Date:	Thu, 02 Dec 2010 10:02:27 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	"hpa@...or.com" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>, sam@...nborg.org,
	eric.dumazet@...il.com
Subject: [patch 2/3] add new macros to make percpu readmostly section
 correctly align

percpu readmostly section should start and end at address cachline aligned.
Idealy we should change PERCPU_VADDR/PERCPU, but I can't change all arch code, so
I add new macros for x86.

Signed-off-by: Shaohua Li <shaohua.li@...el.com>

---
 include/asm-generic/vmlinux.lds.h |   66 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

Index: linux/include/asm-generic/vmlinux.lds.h
===================================================================
--- linux.orig/include/asm-generic/vmlinux.lds.h	2010-12-02 09:22:32.000000000 +0800
+++ linux/include/asm-generic/vmlinux.lds.h	2010-12-02 09:32:42.000000000 +0800
@@ -726,6 +726,72 @@
 		VMLINUX_SYMBOL(__per_cpu_end) = .;			\
 	}
 
+/**
+ * PERCPU_VADDR_CACHEALIGNED - define output section for percpu area
+ * @vaddr: explicit base address (optional)
+ * @phdr: destination PHDR (optional)
+ * @cacheline: cachline size required by readmostly percpu data
+ *
+ * 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.
+ *
+ * @phdr defines the output PHDR to use if not blank.  Be warned that
+ * output PHDR is sticky.  If @phdr is specified, the next output
+ * section in the linker script will go there too.  @phdr should have
+ * a leading colon.
+ *
+ * Note that this macros defines __per_cpu_load as an absolute symbol.
+ * If there is no need to put the percpu section at a predetermined
+ * address, use PERCPU_CACHEALIGNED().
+ */
+#define PERCPU_VADDR_CACHEALIGNED(vaddr, phdr, cacheline)		\
+	VMLINUX_SYMBOL(__per_cpu_load) = .;				\
+	.data..percpu vaddr : AT(VMLINUX_SYMBOL(__per_cpu_load)		\
+				- LOAD_OFFSET) {			\
+		VMLINUX_SYMBOL(__per_cpu_start) = .;			\
+		*(.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) = .;			\
+	} phdr								\
+	. = VMLINUX_SYMBOL(__per_cpu_load) + SIZEOF(.data..percpu);
+
+/**
+ * PERCPU_CACHEALIGNED - define output section for percpu area, simple version
+ * @align: required alignment
+ * @cacheline: cachline size required by readmostly percpu data
+ *
+ * Align to @align and outputs output section for percpu area.  This
+ * macro doesn't maniuplate @vaddr or @phdr and __per_cpu_load and
+ * __per_cpu_start will be identical.
+ *
+ * This macro is equivalent to ALIGN(align); PERCPU_VADDR_CACHEALIGNED( , ) except
+ * that __per_cpu_load is defined as a relative symbol against
+ * .data..percpu which is required for relocatable x86_32
+ * configuration.
+ */
+#define PERCPU_CACHEALIGNED(align, cacheline)				\
+	. = ALIGN(align);						\
+	.data..percpu	: AT(ADDR(.data..percpu) - LOAD_OFFSET) {	\
+		VMLINUX_SYMBOL(__per_cpu_load) = .;			\
+		VMLINUX_SYMBOL(__per_cpu_start) = .;			\
+		*(.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) = .;			\
+	}
 
 /*
  * Definition of the high level *_SECTION macros


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