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authorJohn Hawkes <hawkes@sgi.com>2005-12-16 10:00:24 -0800
committerTony Luck <tony.luck@intel.com>2005-12-16 10:00:24 -0800
commitf5899b5d4fa806403f547dc41312d017d94ec273 (patch)
tree4cbc38474b5ab6dfe8591f0b490686315a6aaa26 /arch/ia64
parent7b6666530e2736f190a2629c8abe34275054449f (diff)
[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 <hawkes@sgi.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
Diffstat (limited to 'arch/ia64')
-rw-r--r--arch/ia64/kernel/time.c29
1 files changed, 29 insertions, 0 deletions
diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c
index 5b7e736f3b49..028a2b95936c 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);

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