The patch titled
percpu: introduce DEFINE_PER_CPU_PAGE_ALIGNED()
has been added to the -mm tree. Its filename is
percpu-introduce-define_per_cpu_page_aligned.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: percpu: introduce DEFINE_PER_CPU_PAGE_ALIGNED()
From: Eric Dumazet <dada1@xxxxxxxxxxxxx>
While examining percpu section on i386 I found we were wasting about 8000
bytes because of two large holes :
c05dd000 D __per_cpu_start
c05dd000 D per_cpu__current_task
c05dd004 D per_cpu__cpu_number
c05dd008 D per_cpu__irq_regs
c05dd00c D per_cpu__x86_cpu_to_apicid
c05dd010 d per_cpu__cpu_devices
c05dd044 D per_cpu__cyc2ns
*HOLE* of 4Kbytes
c05de000 d per_cpu__cpuid4_info
c05de004 d per_cpu__cache_kobject
c05de008 d per_cpu__index_kobject
*HOLE* of 4Kbytes
c05df000 D per_cpu__gdt_page
c05e0000 d per_cpu__next_check
c05e0008 d per_cpu__thermal_throttle_count
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, mixing variables with quite different alignment
requirements.
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.
# size -A vmlinux.old vmlinux | grep percpu
.data.percpu 22272 3227373568
.data.percpu 30336 3227373568
Thats 8064 bytes saved for each CPU (plus one for the .data.percpu storage
itself)
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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 | 11 ++++++++++-
4 files changed, 13 insertions(+), 2 deletions(-)
diff -puN arch/x86/kernel/cpu/common.c~percpu-introduce-define_per_cpu_page_aligned arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~percpu-introduce-define_per_cpu_page_aligned
+++ a/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 -puN arch/x86/kernel/vmlinux_32.lds.S~percpu-introduce-define_per_cpu_page_aligned arch/x86/kernel/vmlinux_32.lds.S
--- a/arch/x86/kernel/vmlinux_32.lds.S~percpu-introduce-define_per_cpu_page_aligned
+++ a/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 -puN include/asm-generic/vmlinux.lds.h~percpu-introduce-define_per_cpu_page_aligned include/asm-generic/vmlinux.lds.h
--- a/include/asm-generic/vmlinux.lds.h~percpu-introduce-define_per_cpu_page_aligned
+++ a/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 -puN include/linux/percpu.h~percpu-introduce-define_per_cpu_page_aligned include/linux/percpu.h
--- a/include/linux/percpu.h~percpu-introduce-define_per_cpu_page_aligned
+++ a/include/linux/percpu.h
@@ -15,19 +15,28 @@
#ifdef MODULE
#define SHARED_ALIGNED_SECTION ".data.percpu"
+#define PAGE_ALIGNED_SECTION ".data.percpu"
#else
#define SHARED_ALIGNED_SECTION ".data.percpu.shared_aligned"
+#define PAGE_ALIGNED_SECTION ".data.percpu.page_aligned"
#endif
#define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \
__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__(PAGE_ALIGNED_SECTION))) \
+ 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 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
_
Patches currently in -mm which might be from dada1@xxxxxxxxxxxxx are
oprofile-dont-request-cache-line-alignment-for-cpu_buffer.patch
per_cpu-fix-define_per_cpu_shared_aligned-for-modules.patch
linux-next.patch
percpu-introduce-define_per_cpu_page_aligned.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
