From e888d7facd1f1460a638151036d15b6cfb3ccc74 Mon Sep 17 00:00:00 2001 From: "Pallipadi, Venkatesh" Date: Thu, 25 Jun 2009 16:44:31 -0700 Subject: [PATCH] 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 Signed-off-by: H. Peter Anvin --- arch/x86/lib/delay.c | 3 +++ 1 file changed, 3 insertions(+) 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); } } -- 2.30.2