softirqs-forced-threading-of-softirqs.patch

From 8acdcc8d9d0a296b89756eb9b76289ff311f6962 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:29:31 -0500
Subject: [PATCH] softirqs: forced threading of softirqs

commit cecf393e7eca1950e4299f21c072617b8f7b568c in tip.

Split them into separate threads. One for each softirq

[PG: original didn't need extra_flags back in 2.6.31, also
 add things like BLOCK_IOPOLL_SOFTIRQ which appeared in 33rt]

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 54c9394..f89e357 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -354,7 +354,6 @@ enum
 	SCHED_SOFTIRQ,
 	HRTIMER_SOFTIRQ,
 	RCU_SOFTIRQ,	/* Preferable RCU should always be the last softirq */
-
 	NR_SOFTIRQS
 };
 
@@ -372,11 +371,14 @@ struct softirq_action
 	void	(*action)(struct softirq_action *);
 };
 
+#define __raise_softirq_irqoff(nr) \
+	do { or_softirq_pending(1UL << (nr)); } while (0)
+#define __do_raise_softirq_irqoff(nr) __raise_softirq_irqoff(nr)
+
 asmlinkage void do_softirq(void);
 asmlinkage void __do_softirq(void);
 extern void open_softirq(int nr, void (*action)(struct softirq_action *));
 extern void softirq_init(void);
-#define __raise_softirq_irqoff(nr) do { or_softirq_pending(1UL << (nr)); } while (0)
 extern void raise_softirq_irqoff(unsigned int nr);
 extern void raise_softirq(unsigned int nr);
 
@@ -524,6 +526,7 @@ extern void tasklet_kill(struct tasklet_struct *t);
 extern void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu);
 extern void tasklet_init(struct tasklet_struct *t,
 			 void (*func)(unsigned long), unsigned long data);
+extern void takeover_tasklets(unsigned int cpu);
 
 struct tasklet_hrtimer {
 	struct hrtimer		timer;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c916409..4807851 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -102,6 +102,12 @@ struct fs_struct;
 struct bts_context;
 struct perf_event_context;
 
+#ifdef CONFIG_PREEMPT_SOFTIRQS
+extern int softirq_preemption;
+#else
+# define softirq_preemption 0
+#endif
+
 /*
  * List of flags we want to share for kernel threads,
  * if only because they are not used by them anyway.
@@ -1234,6 +1240,7 @@ struct task_struct {
 	void *stack;
 	atomic_t usage;
 	unsigned int flags;	/* per process flags, defined below */
+	unsigned int extra_flags;
 	unsigned int ptrace;
 
 	int lock_depth;		/* BKL lock depth */
@@ -1788,6 +1795,9 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #define PF_FREEZER_SKIP	0x40000000	/* Freezer should not count it as freezeable */
 #define PF_FREEZER_NOSIG 0x80000000	/* Freezer won't send signals to it */
 
+/* Flags in the extra_flags field */
+#define PFE_SOFTIRQ	0x00000001	/* softirq context */
+
 /*
  * Only the _current_ task can read/write to tsk->flags, but other
  * tasks can access tsk->flags in readonly mode for example
@@ -2440,6 +2450,8 @@ extern int __cond_resched_softirq(void);
 	__cond_resched_softirq();				\
 })
 
+extern int cond_resched_softirq_context(void);
+
 /*
  * Does a critical section need to be broken due to another
  * task waiting?: (technically does not depend on CONFIG_PREEMPT,
@@ -2471,6 +2483,13 @@ static inline void thread_group_cputime_free(struct signal_struct *sig)
 {
 }
 
+static inline int softirq_need_resched(void)
+{
+	if (softirq_preemption && (current->extra_flags & PFE_SOFTIRQ))
+		return need_resched();
+	return 0;
+}
+
 /*
  * Reevaluate whether the task has signals pending delivery.
  * Wake the task if so.
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index bf987b9..2ff1834 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -52,3 +52,18 @@ config PREEMPT
 
 endchoice
 
+config PREEMPT_SOFTIRQS
+	bool "Thread Softirqs"
+	default n
+#	depends on PREEMPT
+	help
+	  This option reduces the latency of the kernel by 'threading'
+	  soft interrupts. This means that all softirqs will execute
+	  in softirqd's context. While this helps latency, it can also
+	  reduce performance.
+
+	  The threading of softirqs can also be controlled via
+	  /proc/sys/kernel/softirq_preemption runtime flag and the
+	  sofirq-preempt=0/1 boot-time option.
+
+	  Say N if you are unsure.
diff --git a/kernel/sched.c b/kernel/sched.c
index 1c5f49d..b059d2f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5125,7 +5125,7 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
 	tmp = cputime_to_cputime64(cputime);
 	if (hardirq_count() - hardirq_offset)
 		cpustat->irq = cputime64_add(cpustat->irq, tmp);
-	else if (softirq_count())
+	else if (softirq_count() || (p->extra_flags & PFE_SOFTIRQ))
 		cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
 	else
 		cpustat->system = cputime64_add(cpustat->system, tmp);
@@ -5689,7 +5689,7 @@ asmlinkage void __sched preempt_schedule_irq(void)
 	int saved_lock_depth;
 
 	/* Catch callers which need to be fixed */
-	BUG_ON(ti->preempt_count || !irqs_disabled());
+	WARN_ON_ONCE(ti->preempt_count || !irqs_disabled());
 
 	do {
 		add_preempt_count(PREEMPT_ACTIVE);
@@ -6830,9 +6830,12 @@ int __cond_resched_lock(spinlock_t *lock)
 }
 EXPORT_SYMBOL(__cond_resched_lock);
 
+/*
+ * Voluntarily preempt a process context that has softirqs disabled:
+ */
 int __sched __cond_resched_softirq(void)
 {
-	BUG_ON(!in_softirq());
+	WARN_ON_ONCE(!in_softirq());
 
 	if (should_resched()) {
 		local_bh_enable();
@@ -6844,6 +6847,25 @@ int __sched __cond_resched_softirq(void)
 }
 EXPORT_SYMBOL(__cond_resched_softirq);
 
+/*
+ * Voluntarily preempt a softirq context (possible with softirq threading):
+ */
+int __sched cond_resched_softirq_context(void)
+{
+	WARN_ON_ONCE(!in_softirq());
+
+	if (softirq_need_resched() && system_state == SYSTEM_RUNNING) {
+		raw_local_irq_disable();
+		_local_bh_enable();
+		raw_local_irq_enable();
+		__cond_resched();
+		local_bh_disable();
+		return 1;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(cond_resched_softirq_context);
+
 /**
  * yield - yield the current processor to other threads.
  *
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 19ef218..eda9c66 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -8,9 +8,15 @@
  *	Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
  *
  *	Remote softirq infrastructure is by Jens Axboe.
+ *
+ *	Softirq-split implemetation by
+ *	Copyright (C) 2005 Thomas Gleixner, Ingo Molnar
  */
 
 #include <linux/module.h>
+#include <linux/kallsyms.h>
+#include <linux/syscalls.h>
+#include <linux/wait.h>
 #include <linux/kernel_stat.h>
 #include <linux/interrupt.h>
 #include <linux/init.h>
@@ -54,7 +60,14 @@ EXPORT_SYMBOL(irq_stat);
 
 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
 
-static DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
+struct softirqdata {
+	int			nr;
+	unsigned long		cpu;
+	struct task_struct	*tsk;
+	int			running;
+};
+
+static DEFINE_PER_CPU(struct softirqdata [NR_SOFTIRQS], ksoftirqd);
 
 char *softirq_to_name[NR_SOFTIRQS] = {
 	"HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
@@ -67,16 +80,32 @@ char *softirq_to_name[NR_SOFTIRQS] = {
  * to the pending events, so lets the scheduler to balance
  * the softirq load for us.
  */
-static void wakeup_softirqd(void)
+static void wakeup_softirqd(int softirq)
 {
 	/* Interrupts are disabled: no need to stop preemption */
-	struct task_struct *tsk = __get_cpu_var(ksoftirqd);
+	struct task_struct *tsk = __get_cpu_var(ksoftirqd)[softirq].tsk;
 
 	if (tsk && tsk->state != TASK_RUNNING)
 		wake_up_process(tsk);
 }
 
 /*
+ * Wake up the softirq threads which have work
+ */
+static void trigger_softirqs(void)
+{
+	u32 pending = local_softirq_pending();
+	int curr = 0;
+
+	while (pending) {
+		if (pending & 1)
+			wakeup_softirqd(curr);
+		pending >>= 1;
+		curr++;
+	}
+}
+
+/*
  * This one is for softirq.c-internal use,
  * where hardirqs are disabled legitimately:
  */
@@ -188,7 +217,7 @@ EXPORT_SYMBOL(local_bh_enable_ip);
  */
 #define MAX_SOFTIRQ_RESTART 10
 
-asmlinkage void __do_softirq(void)
+static void ___do_softirq(void)
 {
 	struct softirq_action *h;
 	__u32 pending;
@@ -198,9 +227,6 @@ asmlinkage void __do_softirq(void)
 	pending = local_softirq_pending();
 	account_system_vtime(current);
 
-	__local_bh_disable((unsigned long)__builtin_return_address(0));
-	lockdep_softirq_enter();
-
 	cpu = smp_processor_id();
 restart:
 	/* Reset the pending bitmask before enabling irqs */
@@ -228,6 +254,7 @@ restart:
 			}
 
 			rcu_bh_qs(cpu);
+			cond_resched_softirq_context();
 		}
 		h++;
 		pending >>= 1;
@@ -240,12 +267,34 @@ restart:
 		goto restart;
 
 	if (pending)
-		wakeup_softirqd();
+		trigger_softirqs();
+}
+
+asmlinkage void __do_softirq(void)
+{
+#ifdef CONFIG_PREEMPT_SOFTIRQS
+	/*
+	 * 'preempt harder'. Push all softirq processing off to ksoftirqd.
+	 */
+	if (softirq_preemption) {
+		if (local_softirq_pending())
+			trigger_softirqs();
+		return;
+	}
+#endif
+	/*
+	 * 'immediate' softirq execution:
+	 */
+	__local_bh_disable((unsigned long)__builtin_return_address(0));
+	lockdep_softirq_enter();
+
+	___do_softirq();
 
 	lockdep_softirq_exit();
 
 	account_system_vtime(current);
 	_local_bh_enable();
+
 }
 
 #ifndef __ARCH_HAS_DO_SOFTIRQ
@@ -316,19 +365,11 @@ void irq_exit(void)
  */
 inline void raise_softirq_irqoff(unsigned int nr)
 {
-	__raise_softirq_irqoff(nr);
+	__do_raise_softirq_irqoff(nr);
 
-	/*
-	 * If we're in an interrupt or softirq, we're done
-	 * (this also catches softirq-disabled code). We will
-	 * actually run the softirq once we return from
-	 * the irq or softirq.
-	 *
-	 * Otherwise we wake up ksoftirqd to make sure we
-	 * schedule the softirq soon.
-	 */
-	if (!in_interrupt())
-		wakeup_softirqd();
+#ifdef CONFIG_PREEMPT_SOFTIRQS
+	wakeup_softirqd(nr);
+#endif
 }
 
 void raise_softirq(unsigned int nr)
@@ -426,7 +467,7 @@ static void tasklet_action(struct softirq_action *a)
 		t->next = NULL;
 		*__get_cpu_var(tasklet_vec).tail = t;
 		__get_cpu_var(tasklet_vec).tail = &(t->next);
-		__raise_softirq_irqoff(TASKLET_SOFTIRQ);
+		__do_raise_softirq_irqoff(TASKLET_SOFTIRQ);
 		local_irq_enable();
 	}
 }
@@ -461,7 +502,7 @@ static void tasklet_hi_action(struct softirq_action *a)
 		t->next = NULL;
 		*__get_cpu_var(tasklet_hi_vec).tail = t;
 		__get_cpu_var(tasklet_hi_vec).tail = &(t->next);
-		__raise_softirq_irqoff(HI_SOFTIRQ);
+		__do_raise_softirq_irqoff(HI_SOFTIRQ);
 		local_irq_enable();
 	}
 }
@@ -692,33 +733,56 @@ void __init softirq_init(void)
 	open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 }
 
-static int run_ksoftirqd(void * __bind_cpu)
+static int run_ksoftirqd(void * __data)
 {
+	/* Priority needs to be below hardirqs */
+	struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2 - 1};
+	struct softirqdata *data = __data;
+	u32 mask = (1 << data->nr);
+	struct softirq_action *h;
+
+	sys_sched_setscheduler(current->pid, SCHED_FIFO, &param);
+	current->extra_flags |= PFE_SOFTIRQ;
 	set_current_state(TASK_INTERRUPTIBLE);
 
 	while (!kthread_should_stop()) {
 		preempt_disable();
-		if (!local_softirq_pending()) {
+		if (!(local_softirq_pending() & mask)) {
 			preempt_enable_and_schedule();
 			preempt_disable();
 		}
 
 		__set_current_state(TASK_RUNNING);
+		data->running = 1;
 
-		while (local_softirq_pending()) {
+		while (local_softirq_pending() & mask) {
 			/* Preempt disable stops cpu going offline.
 			   If already offline, we'll be on wrong CPU:
 			   don't process */
-			if (cpu_is_offline((long)__bind_cpu))
+			if (cpu_is_offline(data->cpu))
 				goto wait_to_die;
-			do_softirq();
+
+			local_irq_disable();
 			__preempt_enable_no_resched();
+			set_softirq_pending(local_softirq_pending() & ~mask);
+			local_bh_disable();
+			local_irq_enable();
+
+			h = &softirq_vec[data->nr];
+			if (h)
+				h->action(h);
+			rcu_bh_qs(data->cpu);
+
+			local_irq_disable();
+			_local_bh_enable();
+			local_irq_enable();
+
 			cond_resched();
 			preempt_disable();
-			rcu_sched_qs((long)__bind_cpu);
 		}
 		preempt_enable();
 		set_current_state(TASK_INTERRUPTIBLE);
+		data->running = 0;
 	}
 	__set_current_state(TASK_RUNNING);
 	return 0;
@@ -768,7 +832,7 @@ void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 	BUG();
 }
 
-static void takeover_tasklets(unsigned int cpu)
+void takeover_tasklets(unsigned int cpu)
 {
 	/* CPU is dead, so no lock needed. */
 	local_irq_disable();
@@ -794,49 +858,83 @@ static void takeover_tasklets(unsigned int cpu)
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
+static const char *softirq_names [] =
+{
+  [HI_SOFTIRQ]		= "high",
+  [SCHED_SOFTIRQ]	= "sched",
+  [TIMER_SOFTIRQ]	= "timer",
+  [NET_TX_SOFTIRQ]	= "net-tx",
+  [NET_RX_SOFTIRQ]	= "net-rx",
+  [BLOCK_SOFTIRQ]	= "block",
+  [BLOCK_IOPOLL_SOFTIRQ]= "block-iopoll",
+  [TASKLET_SOFTIRQ]	= "tasklet",
+#ifdef CONFIG_HIGH_RES_TIMERS
+  [HRTIMER_SOFTIRQ]	= "hrtimer",
+#endif
+  [RCU_SOFTIRQ]		= "rcu",
+};
+
 static int __cpuinit cpu_callback(struct notifier_block *nfb,
 				  unsigned long action,
 				  void *hcpu)
 {
-	int hotcpu = (unsigned long)hcpu;
+	int hotcpu = (unsigned long)hcpu, i;
 	struct task_struct *p;
 
 	switch (action) {
 	case CPU_UP_PREPARE:
 	case CPU_UP_PREPARE_FROZEN:
-		p = kthread_create(run_ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
-		if (IS_ERR(p)) {
-			printk("ksoftirqd for %i failed\n", hotcpu);
-			return NOTIFY_BAD;
+		for (i = 0; i < NR_SOFTIRQS; i++) {
+			per_cpu(ksoftirqd, hotcpu)[i].nr = i;
+			per_cpu(ksoftirqd, hotcpu)[i].cpu = hotcpu;
+			per_cpu(ksoftirqd, hotcpu)[i].tsk = NULL;
 		}
-		kthread_bind(p, hotcpu);
-  		per_cpu(ksoftirqd, hotcpu) = p;
- 		break;
+		for (i = 0; i < NR_SOFTIRQS; i++) {
+			p = kthread_create(run_ksoftirqd,
+					   &per_cpu(ksoftirqd, hotcpu)[i],
+					   "softirq-%s/%d", softirq_names[i],
+					   hotcpu);
+			if (IS_ERR(p)) {
+				printk("ksoftirqd %d for %i failed\n", i,
+				       hotcpu);
+				return NOTIFY_BAD;
+			}
+			kthread_bind(p, hotcpu);
+			per_cpu(ksoftirqd, hotcpu)[i].tsk = p;
+		}
+		break;
+	break;
 	case CPU_ONLINE:
 	case CPU_ONLINE_FROZEN:
-		wake_up_process(per_cpu(ksoftirqd, hotcpu));
+		for (i = 0; i < NR_SOFTIRQS; i++)
+			wake_up_process(per_cpu(ksoftirqd, hotcpu)[i].tsk);
 		break;
 #ifdef CONFIG_HOTPLUG_CPU
 	case CPU_UP_CANCELED:
 	case CPU_UP_CANCELED_FROZEN:
-		if (!per_cpu(ksoftirqd, hotcpu))
-			break;
-		/* Unbind so it can run.  Fall thru. */
-		kthread_bind(per_cpu(ksoftirqd, hotcpu),
-			     cpumask_any(cpu_online_mask));
+#if 0
+		for (i = 0; i < NR_SOFTIRQS; i++) {
+			if (!per_cpu(ksoftirqd, hotcpu)[i].tsk)
+				continue;
+			kthread_bind(per_cpu(ksoftirqd, hotcpu)[i].tsk,
+				     cpumask_any(cpu_online_mask));
+		}
+#endif
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN: {
 		struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 
-		p = per_cpu(ksoftirqd, hotcpu);
-		per_cpu(ksoftirqd, hotcpu) = NULL;
-		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
-		kthread_stop(p);
+		for (i = 0; i < NR_SOFTIRQS; i++) {
+			p = per_cpu(ksoftirqd, hotcpu)[i].tsk;
+			per_cpu(ksoftirqd, hotcpu)[i].tsk = NULL;
+			sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
+			kthread_stop(p);
+		}
 		takeover_tasklets(hotcpu);
 		break;
 	}
 #endif /* CONFIG_HOTPLUG_CPU */
- 	}
+	}
 	return NOTIFY_OK;
 }
 
@@ -856,6 +954,29 @@ static __init int spawn_ksoftirqd(void)
 }
 early_initcall(spawn_ksoftirqd);
 
+
+#ifdef CONFIG_PREEMPT_SOFTIRQS
+
+int softirq_preemption = 1;
+
+EXPORT_SYMBOL(softirq_preemption);
+
+static int __init softirq_preempt_setup (char *str)
+{
+	if (!strncmp(str, "off", 3))
+		softirq_preemption = 0;
+	else
+		get_option(&str, &softirq_preemption);
+	if (!softirq_preemption)
+		printk("turning off softirq preemption!\n");
+
+	return 1;
+}
+
+__setup("softirq-preempt=", softirq_preempt_setup);
+
+#endif
+
 #ifdef CONFIG_SMP
 /*
  * Call a function on all processors
-- 
1.7.1.1