Hi. I'm investigating preempt patch for 2.4 kernel. (MIPS part of
preempt-kernel-rml-2.4.26-pre5-1.patch seems a bit old. I'm looking
Jun Sun's 030304-b.preempt-mips.patch).
The patch contains following block (end of
arch/mips/kernel/irq.c:do_IRQ()):
if (softirq_pending(cpu))
do_softirq();
+
+#if defined(CONFIG_PREEMPT)
+ for(;;) {
+ preempt_enable_no_resched();
+ if (preempt_is_disabled() || !need_resched())
+ break;
+
+ db_assert(intr_off());
+ db_assert(!in_interrupt());
+
+ preempt_disable();
+ __sti();
+ preempt_schedule();
+ __cli();
+ }
+#endif
+
return 1;
}
Q1. What is purpose of this block? (To decrease latency? But other
archs (and 2.6 MIPS kernel) do not have block like this...)
Q2. If an interrupt happened between __sti() and __cli(), and the
interrupt handler raise softirq, the softirq handler will not be
called soon (because do_softirq() immediately return if preempt
disabled). So we must check softirq_pending again after this block?
Thank you.
---
Atsushi Nemoto
