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SubjectRe: -rt more realtime scheduling issues
On Mon, Oct 08, 2007 at 11:04:12PM -0400, Steven Rostedt wrote:
> On Mon, Oct 08, 2007 at 11:45:23AM -0700, Mike Kravetz wrote:
> > Are these accurate statements? I'll start working on a reliable delivery
> > mechanism for RealTime scheduling. But, I just want to make sure that
> > is really necessary.
>
> For i386 I don't think so. Seems that the interrupt handler will set the
> current task to "need_resched" and on exit of the interrupt handler, the
> schedule should take place. I don't see the race (that doesn't mean
> there is one).

The more I try understand the IPI handling the more confused I get. :(
At fist I was concerned about an IPI happening in the middle of the
__schedule routine. But, then it occurred to me that interrupts are
disabled when in this routine (when holding the runqueue lock). So, IPIs
are not delivered during __schedule processing. Right?

But, if this is case then I don't understand the following code in
schedule():

local_irq_disable();

do {
__schedule();
} while (unlikely(test_thread_flag(TIF_NEED_RESCHED) ||
test_thread_flag(TIF_NEED_RESCHED_DELAYED)));
local_irq_enable();

How can the reschedule flags possibly be set AFTER running __schedule.
Especially when the call is explicitly surrounded by local_irq_disable/
local_irq_enable.

Can someone help me?
--
Mike
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