Re: Problems with CONFIG_PREEMPT

[Jun Sun <jsun@mvista.com>]

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On Tue, Dec 17, 2002 at 08:27:16AM +0000, Colin.Helliwell@Zarlink.Com wrote:
> 
> NEW_TIME_C is set. URL to the patch is:
> http://www.kernel.org/pub/linux/kernel/people/rml/preempt-kernel/v2.4/preempt-kernel-rml-2.4.19-2.patch
>

There are some bits missing.  Not sure if it is related to your problem or not.

Robert, please take the MIPS preemptible kernel update patch.

> We ultimately want to add in real-time support, such as Ingo's O(1)
> scheduler - if this is 'complete' for MIPS. 

O(1) shortens process dispatching time, usually not a big time saver
unless you have *lots* of process and/or you are doing frequent context
switches.

Another patch which is probably more important is the Ingo's breaking
selected big lock patch.  That will preemption work more effectively.

> I don't know if it would be
> better just to go for this in one hit, or if we'd need the preemption
> sorted out anyway first. 

You do have to sort them out one by one.  (Or you get them all by becoming
mvista customer. :-0)

> Or should we just go to a 2.5.x kernel instead?

We'd love to have more people bang on 2.5 MIPS *grin* ...

Jun
 

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Additional patch for MIPS against RML's 2.4.19-2 preemptiable kernel patch.

http://www.kernel.org/pub/linux/kernel/people/rml/preempt-kernel/v2.4/preempt-kernel-rml-2.4.19-2.patch

Jun

diff -Nru link/arch/mips/kernel/irq.c.orig link/arch/mips/kernel/irq.c
--- link/arch/mips/kernel/irq.c.orig	Tue Dec 17 09:44:29 2002
+++ link/arch/mips/kernel/irq.c	Tue Dec 17 09:44:45 2002
@@ -507,13 +507,13 @@
 		}
 
 		current->preempt_count ++;
-		sti();
+		__sti();
 		if (user_mode(regs)) {
 			schedule();
 		} else {
 			preempt_schedule();
 		}
-		cli();
+		__cli();
 	}
 #endif
 
diff -Nru link/arch/mips/kernel/time.c.orig link/arch/mips/kernel/time.c
--- link/arch/mips/kernel/time.c.orig	Mon Dec  2 16:56:03 2002
+++ link/arch/mips/kernel/time.c	Tue Dec 17 09:53:37 2002
@@ -416,6 +416,8 @@
 {
 	int cpu = smp_processor_id();
 
+	preempt_disable();
+
 	irq_enter(cpu, irq);
 	kstat.irqs[cpu][irq]++;
 
@@ -426,12 +428,34 @@
 
 	if (softirq_pending(cpu))
 		do_softirq();
+
+#if defined(CONFIG_PREEMPT)
+        while (--current->preempt_count == 0) {
+                db_assert(intr_off());
+                db_assert(!in_interrupt());
+
+                if (current->need_resched == 0) {
+                        break;
+                }
+
+                current->preempt_count ++;
+                __sti();
+                if (user_mode(regs)) {
+                        schedule();
+                } else {
+                        preempt_schedule();
+                }
+                __cli();
+        }
+#endif
 }
 
 asmlinkage void ll_local_timer_interrupt(int irq, struct pt_regs *regs)
 {
 	int cpu = smp_processor_id();
 
+	preempt_disable();
+
 	irq_enter(cpu, irq);
 	kstat.irqs[cpu][irq]++;
 
@@ -442,6 +466,26 @@
 
 	if (softirq_pending(cpu))
 		do_softirq();
+
+#if defined(CONFIG_PREEMPT)
+	while (--current->preempt_count == 0) {
+		db_assert(intr_off());
+		db_assert(!in_interrupt());
+
+		if (current->need_resched == 0) {
+			break;
+		}
+
+		current->preempt_count ++;
+		__sti();
+		if (user_mode(regs)) {
+			schedule();
+		} else {
+			preempt_schedule();
+		}
+		__cli();
+	}
+#endif
 }
 
 /*
diff -Nru link/include/asm-mips/softirq.h.orig link/include/asm-mips/softirq.h
--- link/include/asm-mips/softirq.h.orig	Tue Dec 17 09:44:29 2002
+++ link/include/asm-mips/softirq.h	Tue Dec 17 09:54:13 2002
@@ -10,6 +10,9 @@
 #ifndef _ASM_SOFTIRQ_H
 #define _ASM_SOFTIRQ_H
 
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+
 #include <asm/atomic.h>
 #include <asm/hardirq.h>