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 <dvlas...@redhat.com> CC: Ingo Molnar <mi...@kernel.org> CC: Andy Lutomirski <l...@amacapital.net> CC: "H. Peter Anvin" <h...@zytor.com> CC: Borislav Petkov <b...@alien8.de> CC: Brian Gerst <brge...@gmail.com> CC: x...@kernel.org CC: linux-kernel@vger.kernel.org --- arch/x86/include/asm/processor.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 19577dd..b55f309 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(); } -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
