From:	 Ingo Molnar <mingo@elte.hu>
To:	 Linus Torvalds <torvalds@transmeta.com>
Subject: [patch] softirq-2.4.6-C3
Date:	 Wed, 6 Jun 2001 10:22:54 +0200 (CEST)
Cc:	 <linux-kernel@vger.kernel.org>,
	 "David S. Miller" <davem@redhat.com>,
	 Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>


a number of softirq.c updates (the patch is still relative to -B4 and
includes all -C2 changes as well):

- do_softirq() does not have to keep irqs disabled when returning.

- in do_softirq(), disable_local_bh() can be done after checking for
  pending softirqs.

- the goto retry thing has no effect on gcc's code, so it's an unnecessery
  complication of the code.

- ditto the in_interrupt() check, no point in doing a goto, gcc optimizes
  this already.

do_softirq() is now a very compact and straightforward function.

	Ingo

--- linux/kernel/softirq.c.orig	Wed Jun  6 09:00:13 2001
+++ linux/kernel/softirq.c	Wed Jun  6 09:56:06 2001
@@ -52,17 +52,17 @@
 	int cpu = smp_processor_id();
 	__u32 pending;
 
-	local_irq_disable();
 	if (in_interrupt())
-		goto out;
+		return;
 
-	local_bh_disable();
+	local_irq_disable();
 
 	pending = softirq_pending(cpu);
 
 	if (pending) {
 		struct softirq_action *h;
 
+		local_bh_disable();
 restart:
 		/* Reset the pending bitmask before enabling irqs */
 		softirq_pending(cpu) = 0;
@@ -82,20 +82,11 @@
 
 		pending = softirq_pending(cpu);
 		if (pending)
-			goto retry;
+			goto restart;
+		__local_bh_enable();
 	}
 
-	__local_bh_enable();
-out:
-
-	/* Leave with locally disabled hard irqs. It is critical to close
-	 * window for infinite recursion, while we help local bh count,
-	 * it protected us. Now we are defenceless.
-	 */
-	return;
-
-retry:
-	goto restart;
+	local_irq_enable();
 }
 
 
--- linux/include/asm-i386/softirq.h.orig	Wed Jun  6 08:51:54 2001
+++ linux/include/asm-i386/softirq.h	Wed Jun  6 09:48:22 2001
@@ -11,10 +11,39 @@
 
 #define local_bh_disable()	cpu_bh_disable(smp_processor_id())
 #define __local_bh_enable()	__cpu_bh_enable(smp_processor_id())
-#define local_bh_enable()	do { int __cpu = smp_processor_id(); if (!--local_bh_count(__cpu) && softirq_pending(__cpu)) { do_softirq(); __sti(); } } while (0)
 #define __cpu_raise_softirq(cpu,nr) set_bit((nr), &softirq_pending(cpu));
 #define raise_softirq(nr) __cpu_raise_softirq(smp_processor_id(), (nr))
 
 #define in_softirq() (local_bh_count(smp_processor_id()) != 0)
+
+/*
+ * NOTE: this assembly code assumes:
+ *
+ *    (char *)&local_bh_count - 8 == (char *)&softirq_pending
+ *
+ * If you change the offsets in irq_stat then you have to
+ * update this code as well.
+ */
+#define local_bh_enable()						\
+do {									\
+	unsigned int *ptr = &local_bh_count(smp_processor_id());	\
+									\
+	if (!--*ptr)							\
+		__asm__ __volatile__ (					\
+			"cmpl $0, -8(%0);"				\
+			"jnz 2f;"					\
+			"1:;"						\
+									\
+			".section .text.lock,\"ax\";"			\
+			"2: pushl %%eax; pushl %%ecx; pushl %%edx;"	\
+			"call do_softirq;"				\
+			"popl %%edx; popl %%ecx; popl %%eax;"		\
+			"jmp 1b;"					\
+			".previous;"					\
+									\
+		: /* no output */					\
+		: "r" (ptr)						\
+		/* no registers clobbered */ );				\
+} while (0)
 
 #endif	/* __ASM_SOFTIRQ_H */
--- linux/include/asm-i386/hardirq.h.orig	Wed Jun  6 09:04:59 2001
+++ linux/include/asm-i386/hardirq.h	Wed Jun  6 09:16:26 2001
@@ -5,7 +5,7 @@
 #include <linux/threads.h>
 #include <linux/irq.h>
 
-/* entry.S is sensitive to the offsets of these fields */
+/* assembly code in softirq.h is sensitive to the offsets of these fields */
 typedef struct {
 	unsigned int __softirq_pending;
 	unsigned int __local_irq_count;
--- linux/arch/i386/kernel/entry.S.orig	Wed Jun  6 08:48:09 2001
+++ linux/arch/i386/kernel/entry.S	Wed Jun  6 08:51:39 2001
@@ -133,18 +133,6 @@
 	movl $-8192, reg; \
 	andl %esp, reg
 
-#ifdef CONFIG_SMP
-#define CHECK_SOFTIRQ \
-	movl processor(%ebx),%eax; \
-	shll $CONFIG_X86_L1_CACHE_SHIFT,%eax; \
-	xorl %ecx,%ecx; \
-	testl SYMBOL_NAME(irq_stat)+4(,%eax),%ecx
-#else
-#define CHECK_SOFTIRQ \
-	xorl %ecx,%ecx; \
-	testl SYMBOL_NAME(irq_stat)+4,%ecx
-#endif
-
 ENTRY(lcall7)
 	pushfl			# We get a different stack layout with call gates,
 	pushl %eax		# which has to be cleaned up later..
@@ -215,9 +203,7 @@
 	call *SYMBOL_NAME(sys_call_table)(,%eax,4)
 	movl %eax,EAX(%esp)		# save the return value
 ENTRY(ret_from_sys_call)
-	cli
-	CHECK_SOFTIRQ
-	jne handle_softirq
+	cli				# need_resched and signals atomic test
 	cmpl $0,need_resched(%ebx)
 	jne reschedule
 	cmpl $0,sigpending(%ebx)
@@ -233,13 +219,6 @@
 	jne v86_signal_return
 	xorl %edx,%edx
 	call SYMBOL_NAME(do_signal)
-#ifdef CONFIG_SMP
-	GET_CURRENT(%ebx)
-#endif
-	cli
-	CHECK_SOFTIRQ
-	je restore_all
-	call SYMBOL_NAME(do_softirq)
 	jmp restore_all
 
 	ALIGN
@@ -248,13 +227,6 @@
 	movl %eax,%esp
 	xorl %edx,%edx
 	call SYMBOL_NAME(do_signal)
-#ifdef CONFIG_SMP
-	GET_CURRENT(%ebx)
-#endif
-	cli
-	CHECK_SOFTIRQ
-	je restore_all
-	call SYMBOL_NAME(do_softirq)
 	jmp restore_all
 
 	ALIGN
@@ -276,8 +248,6 @@
 	ALIGN
 ret_from_exception:
 	cli
-	CHECK_SOFTIRQ
-	jne handle_softirq
 	cmpl $0,need_resched(%ebx)
 	jne reschedule
 	cmpl $0,sigpending(%ebx)
@@ -292,11 +262,6 @@
 	jne ret_from_sys_call
 	jmp restore_all
 
-	ALIGN
-handle_softirq:
-	call SYMBOL_NAME(do_softirq)
-	jmp ret_from_intr
-	
 	ALIGN
 reschedule:
 	call SYMBOL_NAME(schedule)    # test