On Sat, 23 Feb 2002, Matthew Dillon wrote:
> critical_enter() isn't much better then a mutex. It can
> be optimized to get rid of the inline cli & sti however. Actually, it
> can be optimized trivially for i386, all we have to do is check the
> critical nesting count from the interrupt code and set the
> interrupts-disabled bit in the returned (supervisor mode) frame.
>
> critical_enter() and critical_exit() would then be nearly perfect.
My version of it does less than this. I only use it to help implement
spinlocks.
Index: kern_switch.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/kern_switch.c,v
retrieving revision 1.20
diff -u -2 -r1.20 kern_switch.c
--- kern_switch.c 11 Feb 2002 20:37:51 -0000 1.20
+++ kern_switch.c 13 Feb 2002 05:34:20 -0000
@@ -70,14 +70,21 @@
}
-/* Critical sections that prevent preemption. */
+/*-
+ * Critical section handling.
+ * XXX doesn't belong here.
+ *
+ * Entering a critical section only blocks non-fast interrupts.
+ * critical_enter() is similar to splhigh() in a 2-level spl setup under
+ * old versions of FreeBSD.
+ *
+ * Exiting from all critical sections unblocks non-fast interrupts and runs
+ * the handlers of any that were blocked. critical_exit() is similar to
+ * spl(old_level) in a 2-level spl setup under old versions of FreeBSD.
+ */
void
critical_enter(void)
{
- struct thread *td;
- td = curthread;
- if (td->td_critnest == 0)
- td->td_savecrit = cpu_critical_enter();
- td->td_critnest++;
+ curthread->td_critnest++;
}
@@ -85,12 +92,7 @@
critical_exit(void)
{
- struct thread *td;
- td = curthread;
- if (td->td_critnest == 1) {
- td->td_critnest = 0;
- cpu_critical_exit(td->td_savecrit);
- } else
- td->td_critnest--;
+ if (--curthread->td_critnest == 0 && (ipending | spending) != 0)
+ unpend();
}
Bruce
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