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| author | jkim <jkim@FreeBSD.org> | 2011-06-17 21:41:06 +0000 |
|---|---|---|
| committer | jkim <jkim@FreeBSD.org> | 2011-06-17 21:41:06 +0000 |
| commit | 8a9fdbb838682bca3d92ebd804102b651699ab25 (patch) | |
| tree | 26ac1140ee2ae222240b86fc45dea7d39d7f685b | |
| parent | 93d2d762ed960f4b01b6c523ab0b070977a5beea (diff) | |
| download | FreeBSD-src-8a9fdbb838682bca3d92ebd804102b651699ab25.zip FreeBSD-src-8a9fdbb838682bca3d92ebd804102b651699ab25.tar.gz | |
Teach the compiler how to shift TSC value efficiently. As noted in r220631,
some times compiler inserts redundant instructions to preserve unused upper
32 bits even when it is casted to a 32-bit value. Unfortunately, it seems
the problem becomes more serious when it is shifted, especially on amd64.
| -rw-r--r-- | sys/x86/x86/tsc.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c index 70c176a..9501eee 100644 --- a/sys/x86/x86/tsc.c +++ b/sys/x86/x86/tsc.c @@ -461,7 +461,7 @@ init_TSC_tc(void) tsc_timecounter.tc_quality = 1000; init: - for (shift = 0; shift < 32 && (tsc_freq >> shift) > max_freq; shift++) + for (shift = 0; shift < 31 && (tsc_freq >> shift) > max_freq; shift++) ; if (shift > 0) { tsc_timecounter.tc_get_timecount = tsc_get_timecount_low; @@ -579,6 +579,9 @@ tsc_get_timecount(struct timecounter *tc __unused) static u_int tsc_get_timecount_low(struct timecounter *tc) { + uint32_t rv; - return (rdtsc() >> (int)(intptr_t)tc->tc_priv); + __asm __volatile("rdtsc; shrd %%cl, %%edx, %0" + : "=a" (rv) : "c" ((int)(intptr_t)tc->tc_priv) : "edx"); + return (rv); } |
