On Tue, 2004-07-06 at 00:08 -0400, ml@skeletoid.org wrote:
> In the schedule() function, there is this line:
>
> if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
>
> I wonder why the right part is needed.
> PREEMPT_ACTIVE is defined to 0x4000000,
> so, even if preempt_count() return 0,1,2,.. it will always be 0 when we do the
> logical AND with 0x4000000. So !0 become true, therefore the right side is
> always true. Maybe am I missing something?
You are. The preempt count is actually _set_ to PREEMPT_ACTIVE. You
can see this in the very file you referenced.
So the check is not whether or not preempt_count() is returning any
value, but whether or not it has been and'ed (or set to) PREEMPT_ACTIVE.
This flag is used to delineate whether or not the current schedule is
occurring off of a kernel preemption.
Robert Love
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