diff options
Diffstat (limited to 'arch/x86/kernel/vread_tsc_64.c')
-rw-r--r-- | arch/x86/kernel/vread_tsc_64.c | 36 |
1 files changed, 0 insertions, 36 deletions
diff --git a/arch/x86/kernel/vread_tsc_64.c b/arch/x86/kernel/vread_tsc_64.c deleted file mode 100644 index a81aa9e9894c..000000000000 --- a/arch/x86/kernel/vread_tsc_64.c +++ /dev/null | |||
@@ -1,36 +0,0 @@ | |||
1 | /* This code runs in userspace. */ | ||
2 | |||
3 | #define DISABLE_BRANCH_PROFILING | ||
4 | #include <asm/vgtod.h> | ||
5 | |||
6 | notrace cycle_t __vsyscall_fn vread_tsc(void) | ||
7 | { | ||
8 | cycle_t ret; | ||
9 | u64 last; | ||
10 | |||
11 | /* | ||
12 | * Empirically, a fence (of type that depends on the CPU) | ||
13 | * before rdtsc is enough to ensure that rdtsc is ordered | ||
14 | * with respect to loads. The various CPU manuals are unclear | ||
15 | * as to whether rdtsc can be reordered with later loads, | ||
16 | * but no one has ever seen it happen. | ||
17 | */ | ||
18 | rdtsc_barrier(); | ||
19 | ret = (cycle_t)vget_cycles(); | ||
20 | |||
21 | last = VVAR(vsyscall_gtod_data).clock.cycle_last; | ||
22 | |||
23 | if (likely(ret >= last)) | ||
24 | return ret; | ||
25 | |||
26 | /* | ||
27 | * GCC likes to generate cmov here, but this branch is extremely | ||
28 | * predictable (it's just a funciton of time and the likely is | ||
29 | * very likely) and there's a data dependence, so force GCC | ||
30 | * to generate a branch instead. I don't barrier() because | ||
31 | * we don't actually need a barrier, and if this function | ||
32 | * ever gets inlined it will generate worse code. | ||
33 | */ | ||
34 | asm volatile (""); | ||
35 | return last; | ||
36 | } | ||