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| author | George Spelvin <linux@horizon.com> | 2015-06-25 18:44:13 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-07-06 15:23:30 +0200 |
| commit | 5a33fcb8d991209bac0a266ab499e4b53d116cdd (patch) | |
| tree | cb8e11d6e5d7af424898bb33d96f0a492fa10bba | |
| parent | x86/asm/tsc: Remove rdtsc_barrier() (diff) | |
| download | linux-5a33fcb8d991209bac0a266ab499e4b53d116cdd.tar.xz linux-5a33fcb8d991209bac0a266ab499e4b53d116cdd.zip | |
x86/asm/tsc: Save an instruction in DECLARE_ARGS users
Before, the code to do RDTSC looked like:
rdtsc
shl $0x20, %rdx
mov %eax, %eax
or %rdx, %rax
The "mov %eax, %eax" is required to clear the high 32 bits of RAX.
By declaring low and high as 64-bit variables, the code is
simplified to:
rdtsc
shl $0x20,%rdx
or %rdx,%rax
Yes, it's a 2-byte instruction that's not on a critical path,
but there are principles to be upheld.
Every user of EAX_EDX_RET has been checked. I tried to check
users of EAX_EDX_ARGS, but there weren't any, so I deleted it to
be safe.
( There's no benefit to making "high" 64 bits, but it was the
simplest way to proceed. )
Signed-off-by: George Spelvin <linux@horizon.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.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: jacob.jun.pan@linux.intel.com
Link: http://lkml.kernel.org/r/20150618075906.4615.qmail@ns.horizon.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | arch/x86/include/asm/msr.h | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 02bdd6c65017..131eec2ca137 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -47,14 +47,13 @@ static inline unsigned long long native_read_tscp(unsigned int *aux) * it means rax *or* rdx. */ #ifdef CONFIG_X86_64 -#define DECLARE_ARGS(val, low, high) unsigned low, high -#define EAX_EDX_VAL(val, low, high) ((low) | ((u64)(high) << 32)) -#define EAX_EDX_ARGS(val, low, high) "a" (low), "d" (high) +/* Using 64-bit values saves one instruction clearing the high half of low */ +#define DECLARE_ARGS(val, low, high) unsigned long low, high +#define EAX_EDX_VAL(val, low, high) ((low) | (high) << 32) #define EAX_EDX_RET(val, low, high) "=a" (low), "=d" (high) #else #define DECLARE_ARGS(val, low, high) unsigned long long val #define EAX_EDX_VAL(val, low, high) (val) -#define EAX_EDX_ARGS(val, low, high) "A" (val) #define EAX_EDX_RET(val, low, high) "=A" (val) #endif |