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authorDimitri Sivanich <sivanich@sgi.com>2007-08-07 08:49:32 -0500
committerTony Luck <tony.luck@intel.com>2007-08-13 10:17:23 -0700
commit71416bea5afa9e5a6c76c1509ab69c46c857a2bb (patch)
tree24e411bb388bcc00289aca20d9aa88722f8b5cd2 /arch/ia64
parent39d3520c92cf7a28c07229ca00cc35a1e8026c77 (diff)
[IA64] disable irq's and check need_resched before safe_halt
While sending interrupts to a cpu to repeatedly wake a thread, on occasion that thread will take a full timer tick cycle (4002 usec in my case) to wakeup. The problem concerns a race condition in the code around the safe_halt() call in the default_idle() routine. Setting 'nohalt' on the kernel command line causes the long wakeups to disappear. void default_idle (void) { local_irq_enable(); while (!need_resched()) { --> if (can_do_pal_halt) --> safe_halt(); else A timer tick could arrive between the check for !need_resched and the actual call to safe_halt() (which does a pal call to PAL_HALT_LIGHT). By the time the timer tick completes, a thread that might now need to run could get held up for as long as a timer tick waiting for the halted cpu. I'm proposing that we disable irq's and check need_resched again before calling safe_halt(). Does anyone see any problem with this approach? Signed-off-by: Dimitri Sivanich <sivanich@sgi.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
Diffstat (limited to 'arch/ia64')
-rw-r--r--arch/ia64/kernel/process.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index 4158906c45a..c613fc0e91c 100644
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -198,9 +198,13 @@ default_idle (void)
{
local_irq_enable();
while (!need_resched()) {
- if (can_do_pal_halt)
- safe_halt();
- else
+ if (can_do_pal_halt) {
+ local_irq_disable();
+ if (!need_resched()) {
+ safe_halt();
+ }
+ local_irq_enable();
+ } else
cpu_relax();
}
}