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Date: Wed, 4 Apr 2007 11:42:44 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Rui Nuno Capela <rncbc@...bc.org>
Cc: linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: 2.6.21-rc5-rt10 troubles
* Ingo Molnar <mingo@...e.hu> wrote:
> could you try rt11 (which fixes two bad bugs in rt10)? If rt11 freezes
> too then could you try to unapply the attached patch? This patch is
> the main delta between rt5 and rt11. (plus upstream changes but those
> shouldnt matter for this problem)
FYI, i've released -rt12 meanwhile - and the patch to unapply from -rt12
is below.
Ingo
------------------->
Subject: [patch] softirq preemption: optimization
From: Ingo Molnar <mingo@...e.hu>
optimize softirq preemption by allowing a hardirq context to pick up
softirq processing.
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
include/linux/interrupt.h | 1
kernel/irq/manage.c | 24 +++----
kernel/softirq.c | 150 ++++++++++++++++++++++++++++++++++++----------
3 files changed, 131 insertions(+), 44 deletions(-)
Index: linux/include/linux/interrupt.h
===================================================================
--- linux.orig/include/linux/interrupt.h
+++ linux/include/linux/interrupt.h
@@ -266,6 +266,7 @@ struct softirq_action
asmlinkage void do_softirq(void);
extern void open_softirq(int nr, void (*action)(struct softirq_action*), void *data);
extern void softirq_init(void);
+extern void do_softirq_from_hardirq(void);
#ifdef CONFIG_PREEMPT_HARDIRQS
# define __raise_softirq_irqoff(nr) raise_softirq_irqoff(nr)
Index: linux/kernel/irq/manage.c
===================================================================
--- linux.orig/kernel/irq/manage.c
+++ linux/kernel/irq/manage.c
@@ -628,14 +628,17 @@ static void thread_simple_irq(irq_desc_t
unsigned int irq = desc - irq_desc;
irqreturn_t action_ret;
+repeat:
if (action && !desc->depth) {
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, action);
- cond_resched_hardirq_context();
spin_lock_irq(&desc->lock);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
}
+ if (desc->status & IRQ_PENDING)
+ goto repeat;
+
desc->status &= ~IRQ_INPROGRESS;
}
@@ -692,7 +695,6 @@ static void thread_edge_irq(irq_desc_t *
desc->status &= ~IRQ_PENDING;
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, action);
- cond_resched_hardirq_context();
spin_lock_irq(&desc->lock);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
@@ -721,7 +723,6 @@ static void thread_do_irq(irq_desc_t *de
desc->status &= ~IRQ_PENDING;
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, action);
- cond_resched_hardirq_context();
spin_lock_irq(&desc->lock);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
@@ -757,8 +758,6 @@ static void do_hardirq(struct irq_desc *
wake_up(&desc->wait_for_handler);
}
-extern asmlinkage void __do_softirq(void);
-
static int do_irqd(void * __desc)
{
struct sched_param param = { 0, };
@@ -781,16 +780,13 @@ static int do_irqd(void * __desc)
while (!kthread_should_stop()) {
local_irq_disable_nort();
- set_current_state(TASK_INTERRUPTIBLE);
-#ifndef CONFIG_PREEMPT_RT
- irq_enter();
-#endif
- do_hardirq(desc);
-#ifndef CONFIG_PREEMPT_RT
- irq_exit();
-#endif
+ do {
+ set_current_state(TASK_INTERRUPTIBLE);
+ do_hardirq(desc);
+ do_softirq_from_hardirq();
+ } while (current->state == TASK_RUNNING);
+
local_irq_enable_nort();
- cond_resched();
#ifdef CONFIG_SMP
/*
* Did IRQ affinities change?
Index: linux/kernel/softirq.c
===================================================================
--- linux.orig/kernel/softirq.c
+++ linux/kernel/softirq.c
@@ -100,8 +100,26 @@ static void wakeup_softirqd(int softirq)
/* Interrupts are disabled: no need to stop preemption */
struct task_struct *tsk = __get_cpu_var(ksoftirqd)[softirq].tsk;
- if (tsk && tsk->state != TASK_RUNNING)
- wake_up_process(tsk);
+ if (unlikely(!tsk))
+ return;
+#if defined(CONFIG_PREEMPT_SOFTIRQS) && defined(CONFIG_PREEMPT_HARDIRQS)
+ /*
+ * Optimization: if we are in a hardirq thread context, and
+ * if the priority of the softirq thread is the same as the
+ * priority of the hardirq thread, then 'merge' softirq
+ * processing into the hardirq context. (it will later on
+ * execute softirqs via do_softirq_from_hardirq()).
+ * So here we can skip the wakeup and can rely on the hardirq
+ * context processing it later on.
+ */
+ if ((current->flags & PF_HARDIRQ) && !hardirq_count() &&
+ (tsk->normal_prio == current->normal_prio))
+ return;
+#endif
+ /*
+ * Wake up the softirq task:
+ */
+ wake_up_process(tsk);
}
/*
@@ -250,50 +268,100 @@ EXPORT_SYMBOL(local_bh_enable_ip);
* we want to handle softirqs as soon as possible, but they
* should not be able to lock up the box.
*/
-#define MAX_SOFTIRQ_RESTART 10
+#define MAX_SOFTIRQ_RESTART 20
+
+static DEFINE_PER_CPU(u32, softirq_running);
-asmlinkage void ___do_softirq(void)
+static void ___do_softirq(const int same_prio_only)
{
+ int max_restart = MAX_SOFTIRQ_RESTART, max_loops = MAX_SOFTIRQ_RESTART;
+ __u32 pending, available_mask, same_prio_skipped;
struct softirq_action *h;
- __u32 pending;
- int max_restart = MAX_SOFTIRQ_RESTART;
- int cpu;
+ struct task_struct *tsk;
+ int cpu, softirq;
pending = local_softirq_pending();
account_system_vtime(current);
cpu = smp_processor_id();
restart:
+ available_mask = -1;
+ softirq = 0;
+ same_prio_skipped = 0;
/* Reset the pending bitmask before enabling irqs */
set_softirq_pending(0);
- local_irq_enable();
-
h = softirq_vec;
do {
+ u32 softirq_mask = 1 << softirq;
+
if (pending & 1) {
- {
- u32 preempt_count = preempt_count();
- h->action(h);
- if (preempt_count != preempt_count()) {
- print_symbol("BUG: softirq exited %s with wrong preemption count!\n", (unsigned long) h->action);
- printk("entered with %08x, exited with %08x.\n", preempt_count, preempt_count());
- preempt_count() = preempt_count;
+ u32 preempt_count = preempt_count();
+
+#if defined(CONFIG_PREEMPT_SOFTIRQS) && defined(CONFIG_PREEMPT_HARDIRQS)
+ /*
+ * If executed by a same-prio hardirq thread
+ * then skip pending softirqs that belong
+ * to softirq threads with different priority:
+ */
+ if (same_prio_only) {
+ tsk = __get_cpu_var(ksoftirqd)[softirq].tsk;
+ if (tsk && tsk->normal_prio !=
+ current->normal_prio) {
+ same_prio_skipped |= softirq_mask;
+ available_mask &= ~softirq_mask;
+ goto next;
}
}
+#endif
+ /*
+ * Is this softirq already being processed?
+ */
+ if (per_cpu(softirq_running, cpu) & softirq_mask) {
+ available_mask &= ~softirq_mask;
+ goto next;
+ }
+ per_cpu(softirq_running, cpu) |= softirq_mask;
+ local_irq_enable();
+
+ h->action(h);
+ if (preempt_count != preempt_count()) {
+ print_symbol("BUG: softirq exited %s with wrong preemption count!\n", (unsigned long) h->action);
+ printk("entered with %08x, exited with %08x.\n", preempt_count, preempt_count());
+ preempt_count() = preempt_count;
+ }
rcu_bh_qsctr_inc(cpu);
cond_resched_softirq_context();
+ local_irq_disable();
+ per_cpu(softirq_running, cpu) &= ~softirq_mask;
}
+next:
h++;
+ softirq++;
pending >>= 1;
} while (pending);
- local_irq_disable();
-
+ or_softirq_pending(same_prio_skipped);
pending = local_softirq_pending();
- if (pending && --max_restart)
- goto restart;
+ if (pending & available_mask) {
+ if (--max_restart)
+ goto restart;
+ /*
+ * With softirq threading there's no reason not to
+ * finish the workload we have:
+ */
+#ifdef CONFIG_PREEMPT_SOFTIRQS
+ if (--max_loops) {
+ if (printk_ratelimit())
+ printk("INFO: softirq overload: %08x\n", pending);
+ max_restart = MAX_SOFTIRQ_RESTART;
+ goto restart;
+ }
+ if (printk_ratelimit())
+ printk("BUG: softirq loop! %08x\n", pending);
+#endif
+ }
if (pending)
trigger_softirqs();
@@ -321,7 +389,7 @@ asmlinkage void __do_softirq(void)
p_flags = current->flags & PF_HARDIRQ;
current->flags &= ~PF_HARDIRQ;
- ___do_softirq();
+ ___do_softirq(0);
trace_softirq_exit();
@@ -345,20 +413,29 @@ void do_softirq_from_hardirq(void)
if (!local_softirq_pending())
return;
/*
- * 'immediate' softirq execution:
+ * 'immediate' softirq execution, from hardirq context:
*/
+ local_irq_disable();
__local_bh_disable((unsigned long)__builtin_return_address(0));
+#ifndef CONFIG_PREEMPT_SOFTIRQS
+ trace_softirq_enter();
+#endif
p_flags = current->flags & PF_HARDIRQ;
current->flags &= ~PF_HARDIRQ;
+ current->flags |= PF_SOFTIRQ;
- ___do_softirq();
+ ___do_softirq(1);
+#ifndef CONFIG_PREEMPT_SOFTIRQS
trace_softirq_exit();
-
+#endif
account_system_vtime(current);
- _local_bh_enable();
current->flags |= p_flags;
+ current->flags &= ~PF_SOFTIRQ;
+
+ _local_bh_enable();
+ local_irq_enable();
}
#ifndef __ARCH_HAS_DO_SOFTIRQ
@@ -669,8 +746,9 @@ static int ksoftirqd(void * __data)
{
struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2 };
struct softirqdata *data = __data;
- u32 mask = (1 << data->nr);
+ u32 softirq_mask = (1 << data->nr);
struct softirq_action *h;
+ int cpu = data->cpu;
sys_sched_setscheduler(current->pid, SCHED_FIFO, ¶m);
// set_user_nice(current, -10);
@@ -684,7 +762,8 @@ static int ksoftirqd(void * __data)
while (!kthread_should_stop()) {
preempt_disable();
- if (!(local_softirq_pending() & mask)) {
+ if (!(local_softirq_pending() & softirq_mask)) {
+sleep_more:
__preempt_enable_no_resched();
schedule();
preempt_disable();
@@ -694,16 +773,26 @@ static int ksoftirqd(void * __data)
#endif
__set_current_state(TASK_RUNNING);
- while (local_softirq_pending() & mask) {
+ while (local_softirq_pending() & softirq_mask) {
/* Preempt disable stops cpu going offline.
If already offline, we'll be on wrong CPU:
don't process */
- if (cpu_is_offline(data->cpu))
+ if (cpu_is_offline(cpu))
goto wait_to_die;
local_irq_disable();
+ /*
+ * Is the softirq already being executed by
+ * a hardirq context?
+ */
+ if (per_cpu(softirq_running, cpu) & softirq_mask) {
+ local_irq_enable();
+ set_current_state(TASK_INTERRUPTIBLE);
+ goto sleep_more;
+ }
+ per_cpu(softirq_running, cpu) |= softirq_mask;
__preempt_enable_no_resched();
- set_softirq_pending(local_softirq_pending() & ~mask);
+ set_softirq_pending(local_softirq_pending() & ~softirq_mask);
local_bh_disable();
local_irq_enable();
@@ -713,6 +802,7 @@ static int ksoftirqd(void * __data)
rcu_bh_qsctr_inc(data->cpu);
local_irq_disable();
+ per_cpu(softirq_running, cpu) &= ~softirq_mask;
_local_bh_enable();
local_irq_enable();
-
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