From 71416bea5afa9e5a6c76c1509ab69c46c857a2bb Mon Sep 17 00:00:00 2001 From: Dimitri Sivanich Date: Tue, 7 Aug 2007 08:49:32 -0500 Subject: [PATCH] [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 Signed-off-by: Tony Luck --- arch/ia64/kernel/process.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c index 4158906c45aa..c613fc0e91cc 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(); } }