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![Jiri Olsa](/assets/img/avatar_default.png)
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>
43 lines
1.2 KiB
C
43 lines
1.2 KiB
C
#ifndef _ASM_GENERIC_SECTIONS_H_
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#define _ASM_GENERIC_SECTIONS_H_
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/* References to section boundaries */
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extern char _text[], _stext[], _etext[];
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extern char _data[], _sdata[], _edata[];
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extern char __bss_start[], __bss_stop[];
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extern char __init_begin[], __init_end[];
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extern char _sinittext[], _einittext[];
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extern char _end[];
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extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[];
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extern char __kprobes_text_start[], __kprobes_text_end[];
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extern char __entry_text_start[], __entry_text_end[];
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extern char __initdata_begin[], __initdata_end[];
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extern char __start_rodata[], __end_rodata[];
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/* Start and end of .ctors section - used for constructor calls. */
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extern char __ctors_start[], __ctors_end[];
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/* function descriptor handling (if any). Override
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* in asm/sections.h */
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#ifndef dereference_function_descriptor
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#define dereference_function_descriptor(p) (p)
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#endif
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/* random extra sections (if any). Override
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* in asm/sections.h */
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#ifndef arch_is_kernel_text
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static inline int arch_is_kernel_text(unsigned long addr)
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{
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return 0;
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}
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#endif
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#ifndef arch_is_kernel_data
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static inline int arch_is_kernel_data(unsigned long addr)
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{
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return 0;
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}
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#endif
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#endif /* _ASM_GENERIC_SECTIONS_H_ */
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