From f5899b5d4fa806403f547dc41312d017d94ec273 Mon Sep 17 00:00:00 2001 From: John Hawkes Date: Fri, 16 Dec 2005 10:00:24 -0800 Subject: [IA64] disable preemption in udelay() The udelay() inline for ia64 uses the ITC. If CONFIG_PREEMPT is enabled and the platform has unsynchronized ITCs and the calling task migrates to another CPU while doing the udelay loop, then the effective delay may be too short or very, very long. This patch disables preemption around 100 usec chunks of the overall desired udelay time. This minimizes preemption-holdoffs. udelay() is now too big to be inline, move it out of line and export it. Signed-off-by: John Hawkes Signed-off-by: Tony Luck --- arch/ia64/kernel/time.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) (limited to 'arch/ia64/kernel/time.c') diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c index 5b7e736f3b4..028a2b95936 100644 --- a/arch/ia64/kernel/time.c +++ b/arch/ia64/kernel/time.c @@ -249,3 +249,32 @@ time_init (void) */ set_normalized_timespec(&wall_to_monotonic, -xtime.tv_sec, -xtime.tv_nsec); } + +#define SMALLUSECS 100 + +void +udelay (unsigned long usecs) +{ + unsigned long start; + unsigned long cycles; + unsigned long smallusecs; + + /* + * Execute the non-preemptible delay loop (because the ITC might + * not be synchronized between CPUS) in relatively short time + * chunks, allowing preemption between the chunks. + */ + while (usecs > 0) { + smallusecs = (usecs > SMALLUSECS) ? SMALLUSECS : usecs; + preempt_disable(); + cycles = smallusecs*local_cpu_data->cyc_per_usec; + start = ia64_get_itc(); + + while (ia64_get_itc() - start < cycles) + cpu_relax(); + + preempt_enable(); + usecs -= smallusecs; + } +} +EXPORT_SYMBOL(udelay); -- cgit v1.2.3