From: Denys Vlasenko Date: Thu, 24 Sep 2015 12:02:29 +0000 (+0200) Subject: x86/asm: Force inlining of cpu_relax() X-Git-Tag: firefly_0821_release~176^2~828^2~43 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=0b101e62afe626ecae60173f92f1e0ec72151653;p=firefly-linux-kernel-4.4.55.git x86/asm: Force inlining of cpu_relax() 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: (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 Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner 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 --- diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 19577dd325fa..b55f30960554 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -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(); }