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authorPallipadi, Venkatesh <venkatesh.pallipadi@intel.com>2009-06-26 03:44:31 +0400
committerH. Peter Anvin <hpa@zytor.com>2009-06-26 03:47:40 +0400
commite888d7facd1f1460a638151036d15b6cfb3ccc74 (patch)
tree7d623ee1b31d431317e87f59013a67d8549b9fae /arch/x86/lib
parent658dbfeb5e7ab35d440c665d643a6285e43fddcd (diff)
downloadlinux-e888d7facd1f1460a638151036d15b6cfb3ccc74.tar.xz
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')
-rw-r--r--arch/x86/lib/delay.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
index f4568605d7d5..ff485d361182 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);
}
}