openkylin
/
linux
mirror of https://gitee.com/openkylin/linux.git
9
0
Fork 0
Code Issues Projects Releases Wiki Activity

x86: Add new static_cpu_has() function using alternatives 

For CPU-feature-specific code that touches performance-critical paths,
introduce a static patching version of [boot_]cpu_has().  This is run
at alternatives time and is therefore not appropriate for most
initialization code, but on the other hand initialization code is
generally not performance critical.

On gcc 4.5+ this uses the new "asm goto" feature.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1273135546-29690-2-git-send-email-avi@redhat.com>
This commit is contained in:
H. Peter Anvin 2010-05-11 17:47:07 -07:00
parent dce8bf4e11
commit a3c8acd043
1 changed files with 57 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
arch/x86/include/asm/cpufeature.h
View File

@ -175,6 +175,7 @@
#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
#include <asm/asm.h>
#include <linux/bitops.h>
extern const char * const x86_cap_flags[NCAPINTS*32];
@ -283,6 +284,62 @@ extern const char * const x86_power_flags[32];
#endif /* CONFIG_X86_64 */
/*
* Static testing of CPU features. Used the same as boot_cpu_has().
* These are only valid after alternatives have run, but will statically
* patch the target code for additional performance.
*
*/
static __always_inline __pure bool __static_cpu_has(u8 bit)
{
#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
asm goto("1: jmp %l[t_no]\n"
"2:\n"
".section .altinstructions,\"a\"\n"
_ASM_ALIGN "\n"
_ASM_PTR "1b\n"
_ASM_PTR "0\n" /* no replacement */
" .byte %P0\n" /* feature bit */
" .byte 2b - 1b\n" /* source len */
" .byte 0\n" /* replacement len */
" .byte 0xff + 0 - (2b-1b)\n" /* padding */
".previous\n"
: : "i" (bit) : : t_no);
return true;
t_no:
return false;
#else
u8 flag;
/* Open-coded due to __stringify() in ALTERNATIVE() */
asm volatile("1: movb $0,%0\n"
"2:\n"
".section .altinstructions,\"a\"\n"
_ASM_ALIGN "\n"
_ASM_PTR "1b\n"
_ASM_PTR "3f\n"
" .byte %P1\n" /* feature bit */
" .byte 2b - 1b\n" /* source len */
" .byte 4f - 3f\n" /* replacement len */
" .byte 0xff + (4f-3f) - (2b-1b)\n" /* padding */
".previous\n"
".section .altinstr_replacement,\"ax\"\n"
"3: movb $1,%0\n"
"4:\n"
".previous\n"
: "=qm" (flag) : "i" (bit));
return flag;
#endif
}
#define static_cpu_has(bit) \
( \
__builtin_constant_p(boot_cpu_has(bit)) ? \
boot_cpu_has(bit) : \
(__builtin_constant_p(bit) && !((bit) & ~0xff)) ? \
__static_cpu_has(bit) : \
boot_cpu_has(bit) \
)
#endif /* defined(__KERNEL__) && !defined(__ASSEMBLY__) */
#endif /* _ASM_X86_CPUFEATURE_H */