Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=71416bea5afa9e5a6c76c1509ab69c46c857a2bb
Commit: 71416bea5afa9e5a6c76c1509ab69c46c857a2bb
Parent: 39d3520c92cf7a28c07229ca00cc35a1e8026c77
Author: Dimitri Sivanich <[EMAIL PROTECTED]>
AuthorDate: Tue Aug 7 08:49:32 2007 -0500
Committer: Tony Luck <[EMAIL PROTECTED]>
CommitDate: Mon Aug 13 10:17:23 2007 -0700
[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 <[EMAIL PROTECTED]>
Signed-off-by: Tony Luck <[EMAIL PROTECTED]>
---
arch/ia64/kernel/process.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index 4158906..c613fc0 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();
}
}
-
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