From 63cc8c75156462d4b42cbdd76c293b7eee7ddbfe Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 12 May 2008 15:44:40 +0200 Subject: [PATCH] percpu: introduce DEFINE_PER_CPU_PAGE_ALIGNED() macro While examining holes in percpu section I found this : c05f5000 D per_cpu__current_task c05f5000 D __per_cpu_start c05f5004 D per_cpu__cpu_number c05f5008 D per_cpu__irq_regs c05f500c d per_cpu__cpu_devices c05f5040 D per_cpu__cyc2ns c05f6000 d per_cpu__cpuid4_info c05f6004 d per_cpu__cache_kobject c05f6008 d per_cpu__index_kobject c05f7000 D per_cpu__gdt_page This is because gdt_page is a percpu variable, defined with a page alignement, and linker is doing its job, two times because of .o nesting in the build process. I introduced a new macro DEFINE_PER_CPU_PAGE_ALIGNED() to avoid wasting this space. All page aligned variables (only one at this time) are put in a separate subsection .data.percpu.page_aligned, at the very begining of percpu zone. Before patch , on a x86_32 machine : .data.percpu 30232 3227471872 .data.percpu 22168 3227471872 Thats 8064 bytes saved for each CPU. Signed-off-by: Eric Dumazet Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- arch/x86/kernel/cpu/common.c | 2 +- arch/x86/kernel/vmlinux_32.lds.S | 1 + include/asm-generic/vmlinux.lds.h | 1 + include/linux/percpu.h | 7 +++++++ 4 files changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index d0463a946247..b2f54fafb8bc 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -21,7 +21,7 @@ #include "cpu.h" -DEFINE_PER_CPU(struct gdt_page, gdt_page) = { .gdt = { +DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = { [GDT_ENTRY_KERNEL_CS] = { { { 0x0000ffff, 0x00cf9a00 } } }, [GDT_ENTRY_KERNEL_DS] = { { { 0x0000ffff, 0x00cf9200 } } }, [GDT_ENTRY_DEFAULT_USER_CS] = { { { 0x0000ffff, 0x00cffa00 } } }, diff --git a/arch/x86/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S index ce5ed083a1e9..0f7c29a8c4ea 100644 --- a/arch/x86/kernel/vmlinux_32.lds.S +++ b/arch/x86/kernel/vmlinux_32.lds.S @@ -189,6 +189,7 @@ SECTIONS . = ALIGN(PAGE_SIZE); .data.percpu : AT(ADDR(.data.percpu) - LOAD_OFFSET) { __per_cpu_start = .; + *(.data.percpu.page_aligned) *(.data.percpu) *(.data.percpu.shared_aligned) __per_cpu_end = .; diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index f054778e916c..69e5c1182fde 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -348,6 +348,7 @@ . = ALIGN(align); \ __per_cpu_start = .; \ .data.percpu : AT(ADDR(.data.percpu) - LOAD_OFFSET) { \ + *(.data.percpu.page_aligned) \ *(.data.percpu) \ *(.data.percpu.shared_aligned) \ } \ diff --git a/include/linux/percpu.h b/include/linux/percpu.h index 4cdd393e71e1..2edacc8e6b8b 100644 --- a/include/linux/percpu.h +++ b/include/linux/percpu.h @@ -23,12 +23,19 @@ __attribute__((__section__(SHARED_ALIGNED_SECTION))) \ PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name \ ____cacheline_aligned_in_smp + +#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \ + __attribute__((__section__(".data.percpu.page_aligned"))) \ + PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name #else #define DEFINE_PER_CPU(type, name) \ PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \ DEFINE_PER_CPU(type, name) + +#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \ + DEFINE_PER_CPU(type, name) #endif #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var) -- GitLab