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author | Pallipadi, Venkatesh <venkatesh.pallipadi@intel.com> | 2009-06-25 16:44:31 -0700 |
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committer | H. Peter Anvin <hpa@zytor.com> | 2009-06-25 16:47:40 -0700 |
commit | e888d7facd1f1460a638151036d15b6cfb3ccc74 (patch) | |
tree | 7d623ee1b31d431317e87f59013a67d8549b9fae /arch/x86/lib/delay.c | |
parent | 658dbfeb5e7ab35d440c665d643a6285e43fddcd (diff) | |
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x86, delay: tsc based udelay should have rdtsc_barrier
delay_tsc needs rdtsc_barrier to provide proper delay.
Output from a test driver using hpet to cross check delay
provided by udelay().
Before:
[ 86.794363] Expected delay 5us actual 4679ns
[ 87.154362] Expected delay 5us actual 698ns
[ 87.514162] Expected delay 5us actual 4539ns
[ 88.653716] Expected delay 5us actual 4539ns
[ 94.664106] Expected delay 10us actual 9638ns
[ 95.049351] Expected delay 10us actual 10126ns
[ 95.416110] Expected delay 10us actual 9568ns
[ 95.799216] Expected delay 10us actual 9638ns
[ 103.624104] Expected delay 10us actual 9707ns
[ 104.020619] Expected delay 10us actual 768ns
[ 104.419951] Expected delay 10us actual 9707ns
After:
[ 50.983320] Expected delay 5us actual 5587ns
[ 51.261807] Expected delay 5us actual 5587ns
[ 51.565715] Expected delay 5us actual 5657ns
[ 51.861171] Expected delay 5us actual 5587ns
[ 52.164704] Expected delay 5us actual 5726ns
[ 52.487457] Expected delay 5us actual 5657ns
[ 52.789338] Expected delay 5us actual 5726ns
[ 57.119680] Expected delay 10us actual 10755ns
[ 57.893997] Expected delay 10us actual 10615ns
[ 58.261287] Expected delay 10us actual 10755ns
[ 58.620505] Expected delay 10us actual 10825ns
[ 58.941035] Expected delay 10us actual 10755ns
[ 59.320903] Expected delay 10us actual 10615ns
[ 61.306311] Expected delay 10us actual 10755ns
[ 61.520542] Expected delay 10us actual 10615ns
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/lib/delay.c')
-rw-r--r-- | arch/x86/lib/delay.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c index f456860..ff485d3 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -55,8 +55,10 @@ static void delay_tsc(unsigned long loops) preempt_disable(); cpu = smp_processor_id(); + rdtsc_barrier(); rdtscl(bclock); for (;;) { + rdtsc_barrier(); rdtscl(now); if ((now - bclock) >= loops) break; @@ -78,6 +80,7 @@ static void delay_tsc(unsigned long loops) if (unlikely(cpu != smp_processor_id())) { loops -= (now - bclock); cpu = smp_processor_id(); + rdtsc_barrier(); rdtscl(bclock); } } |