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x86/asm: Force inlining of cpu_relax()

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On x86, cpu_relax() simply calls rep_nop(), which generates one
instruction, PAUSE (aka REP NOP).

With this config:

  http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os

gcc-4.7.2 does not always inline rep_nop(): it generates several
copies of this:

  <rep_nop> (16 copies, 194 calls):
       55                      push   %rbp
       48 89 e5                mov    %rsp,%rbp
       f3 90                   pause
       5d                      pop    %rbp
       c3                      retq

See: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66122

This patch fixes this via s/inline/__always_inline/
on rep_nop() and cpu_relax().

( Forcing inlining only on rep_nop() causes GCC to
  deinline cpu_relax(), with almost no change in generated code).

      text     data      bss       dec     hex filename
  88118971 19905208 36421632 144445811 89c1173 vmlinux.before
  88118139 19905208 36421632 144444979 89c0e33 vmlinux

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1443096149-27291-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Denys Vlasenko 2015-09-24 14:02:29 +02:00 committed by Ingo Molnar
parent 3f2c5085ed
commit 0b101e62af
1 changed files with 2 additions and 2 deletions
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4
arch/x86/include/asm/processor.h
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@ -556,12 +556,12 @@ static inline unsigned int cpuid_edx(unsigned int op)
}
/* REP NOP (PAUSE) is a good thing to insert into busy-wait loops. */
static inline void rep_nop(void)
static __always_inline void rep_nop(void)
{
asm volatile("rep; nop" ::: "memory");
}
static inline void cpu_relax(void)
static __always_inline void cpu_relax(void)
{
rep_nop();
}