Title: [6826] trunk/arch/blackfin/kernel/entry.S: Blackfin: allow high priority domains to preempt schedule_tail()
- Revision
- 6826
- Author
- vapier
- Date
- 2009-06-22 13:19:45 -0500 (Mon, 22 Jun 2009)
Log Message
Blackfin: allow high priority domains to preempt schedule_tail()
ret_from_fork is always entered with hw interrupts off, which prevents
real-time domains to preempt the Linux kernel during part of the
initial context switch to the new task, which could in turn raise the
worst-case latency figures.
To avoid this, stall the root domain stage in the interrupt pipeline
to keep the scheduling tail code free from Linux-handled IRQs, then
enable hardware interrupts again.
Modified Paths
Diff
Modified: trunk/arch/blackfin/kernel/entry.S (6825 => 6826)
--- trunk/arch/blackfin/kernel/entry.S 2009-06-22 18:19:28 UTC (rev 6825)
+++ trunk/arch/blackfin/kernel/entry.S 2009-06-22 18:19:45 UTC (rev 6826)
@@ -43,8 +43,28 @@
ENTRY(_ret_from_fork)
#ifdef CONFIG_IPIPE
- [--sp] = reti; /* IRQs on. */
- SP += 4;
+ /*
+ * Hw IRQs are off on entry, and we don't want the scheduling tail
+ * code to starve high priority domains from interrupts while it
+ * runs. Therefore we first stall the root stage to have the
+ * virtual interrupt state reflect IMASK.
+ */
+ p0.l = ___ipipe_root_status;
+ p0.h = ___ipipe_root_status;
+ r4 = [p0];
+ bitset(r4, 0);
+ [p0] = r4;
+ /*
+ * Then we may enable hw IRQs, allowing preemption from high
+ * priority domains. schedule_tail() will do local_irq_enable()
+ * since Blackfin does not define __ARCH_WANT_UNLOCKED_CTXSW, so
+ * there is no need to unstall the root domain by ourselves
+ * afterwards.
+ */
+ p0.l = _bfin_irq_flags;
+ p0.h = _bfin_irq_flags;
+ r4 = [p0];
+ sti r4;
#endif /* CONFIG_IPIPE */
SP += -12;
call _schedule_tail;
_______________________________________________
Linux-kernel-commits mailing list
[email protected]
https://blackfin.uclinux.org/mailman/listinfo/linux-kernel-commits
