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x86: Separate out entry text section 

Put x86 entry code into a separate link section: .entry.text.

Separating the entry text section seems to have performance
benefits - caused by more efficient instruction cache usage.

Running hackbench with perf stat --repeat showed that the change
compresses the icache footprint. The icache load miss rate went
down by about 15%:

 before patch:
         19417627  L1-icache-load-misses      ( +-   0.147% )

 after patch:
         16490788  L1-icache-load-misses      ( +-   0.180% )

The motivation of the patch was to fix a particular kprobes
bug that relates to the entry text section, the performance
advantage was discovered accidentally.

Whole perf output follows:

 - results for current tip tree:

  Performance counter stats for './hackbench/hackbench 10' (500 runs):

         19417627  L1-icache-load-misses      ( +-   0.147% )
       2676914223  instructions             #      0.497 IPC     ( +- 0.079% )
       5389516026  cycles                     ( +-   0.144% )

      0.206267711  seconds time elapsed   ( +-   0.138% )

 - results for current tip tree with the patch applied:

  Performance counter stats for './hackbench/hackbench 10' (500 runs):

         16490788  L1-icache-load-misses      ( +-   0.180% )
       2717734941  instructions             #      0.502 IPC     ( +- 0.079% )
       5414756975  cycles                     ( +-   0.148% )

      0.206747566  seconds time elapsed   ( +-   0.137% )

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: masami.hiramatsu.pt@hitachi.com
Cc: ananth@in.ibm.com
Cc: davem@davemloft.net
Cc: 2nddept-manager@sdl.hitachi.co.jp
LKML-Reference: <20110307181039.GB15197@jolsa.redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Jiri Olsa 2011-03-07 19:10:39 +01:00 committed by Ingo Molnar
parent 86cb2ec7b2
commit ea7145477a
6 changed files with 18 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/ia32/ia32entry.S
View File

@ -25,6 +25,8 @@
#define sysretl_audit ia32_ret_from_sys_call
#endif
.section .entry.text, "ax"
#define IA32_NR_syscalls ((ia32_syscall_end - ia32_sys_call_table)/8)
.macro IA32_ARG_FIXUP noebp=0

6
arch/x86/kernel/entry_32.S
View File

@ -65,6 +65,8 @@
#define sysexit_audit syscall_exit_work
#endif
.section .entry.text, "ax"
/*
* We use macros for low-level operations which need to be overridden
* for paravirtualization. The following will never clobber any registers:
@ -788,7 +790,7 @@ ENDPROC(ptregs_clone)
*/
.section .init.rodata,"a"
ENTRY(interrupt)
.text
.section .entry.text, "ax"
.p2align 5
.p2align CONFIG_X86_L1_CACHE_SHIFT
ENTRY(irq_entries_start)
@ -807,7 +809,7 @@ vector=FIRST_EXTERNAL_VECTOR
.endif
.previous
.long 1b
.text
.section .entry.text, "ax"
vector=vector+1
.endif
.endr

6
arch/x86/kernel/entry_64.S
View File

@ -61,6 +61,8 @@
#define __AUDIT_ARCH_LE 0x40000000
.code64
.section .entry.text, "ax"
#ifdef CONFIG_FUNCTION_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(mcount)
@ -744,7 +746,7 @@ END(stub_rt_sigreturn)
*/
.section .init.rodata,"a"
ENTRY(interrupt)
.text
.section .entry.text
.p2align 5
.p2align CONFIG_X86_L1_CACHE_SHIFT
ENTRY(irq_entries_start)
@ -763,7 +765,7 @@ vector=FIRST_EXTERNAL_VECTOR
.endif
.previous
.quad 1b
.text
.section .entry.text
vector=vector+1
.endif
.endr

1
arch/x86/kernel/vmlinux.lds.S
View File

@ -105,6 +105,7 @@ SECTIONS
SCHED_TEXT
LOCK_TEXT
KPROBES_TEXT
ENTRY_TEXT
IRQENTRY_TEXT
*(.fixup)
*(.gnu.warning)

1
include/asm-generic/sections.h
View File

@ -11,6 +11,7 @@ extern char _sinittext[], _einittext[];
extern char _end[];
extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[];
extern char __kprobes_text_start[], __kprobes_text_end[];
extern char __entry_text_start[], __entry_text_end[];
extern char __initdata_begin[], __initdata_end[];
extern char __start_rodata[], __end_rodata[];

6
include/asm-generic/vmlinux.lds.h
View File

@ -424,6 +424,12 @@
*(.kprobes.text) \
VMLINUX_SYMBOL(__kprobes_text_end) = .;
#define ENTRY_TEXT \
ALIGN_FUNCTION(); \
VMLINUX_SYMBOL(__entry_text_start) = .; \
*(.entry.text) \
VMLINUX_SYMBOL(__entry_text_end) = .;
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
#define IRQENTRY_TEXT \
ALIGN_FUNCTION(); \