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SubjectRe: [patch] softirq performance fixes, cleanups, 2.4.10.

On Wed, 26 Sep 2001, Russell King wrote:

> The generic definition is the one to use [...]

right, i forgot, thanks for pointing it out. New patch attached that
removes all the old definitions from other architectures and makes the
generic version unconditional.

Ingo
--- linux/kernel/ksyms.c.orig Wed Sep 26 17:04:40 2001
+++ linux/kernel/ksyms.c Wed Sep 26 17:04:48 2001
@@ -538,8 +538,6 @@
EXPORT_SYMBOL(tasklet_kill);
EXPORT_SYMBOL(__run_task_queue);
EXPORT_SYMBOL(do_softirq);
-EXPORT_SYMBOL(raise_softirq);
-EXPORT_SYMBOL(cpu_raise_softirq);
EXPORT_SYMBOL(__tasklet_schedule);
EXPORT_SYMBOL(__tasklet_hi_schedule);

--- linux/kernel/sched.c.orig Wed Sep 26 17:04:40 2001
+++ linux/kernel/sched.c Wed Sep 26 17:04:48 2001
@@ -366,6 +366,28 @@
}

/**
+ * unwakeup - undo wakeup if possible.
+ * @p: task
+ * @state: new task state
+ *
+ * Undo a previous wakeup of the specified task - if the process
+ * is not running already. The main interface to be used is
+ * unwakeup_process(), it will do a lockless test whether the task
+ * is on the runqueue.
+ */
+void __unwakeup_process(struct task_struct * p, long state)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&runqueue_lock, flags);
+ if (!p->has_cpu && (p != current) && task_on_runqueue(p)) {
+ del_from_runqueue(p);
+ p->state = state;
+ }
+ spin_unlock_irqrestore(&runqueue_lock, flags);
+}
+
+/**
* schedule_timeout - sleep until timeout
* @timeout: timeout value in jiffies
*
--- linux/kernel/softirq.c.orig Wed Sep 26 17:04:40 2001
+++ linux/kernel/softirq.c Wed Sep 26 17:45:00 2001
@@ -58,12 +58,35 @@
wake_up_process(tsk);
}

+/*
+ * If a softirqs were fully handled after ksoftirqd was woken
+ * up then try to undo the wakeup.
+ */
+static inline void unwakeup_softirqd(unsigned cpu)
+{
+ struct task_struct * tsk = ksoftirqd_task(cpu);
+
+ if (tsk)
+ unwakeup_process(tsk, TASK_INTERRUPTIBLE);
+}
+
+/*
+ * We restart softirq processing MAX_SOFTIRQ_RESTART times,
+ * and we fall back to softirqd after that.
+ *
+ * This number has been established via experimentation.
+ * The two things to balance is latency against fairness -
+ * 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
+
asmlinkage void do_softirq()
{
+ int max_restart = MAX_SOFTIRQ_RESTART;
int cpu = smp_processor_id();
- __u32 pending;
+ __u32 pending, mask;
long flags;
- __u32 mask;

if (in_interrupt())
return;
@@ -95,55 +118,37 @@
local_irq_disable();

pending = softirq_pending(cpu);
- if (pending & mask) {
- mask &= ~pending;
+ if (pending && --max_restart)
goto restart;
- }
__local_bh_enable();

if (pending)
+ /*
+ * In the normal case ksoftirqd is rarely activated,
+ * increased scheduling hurts performance.
+ * It's a safety measure: if external load starts
+ * to flood the system with softirqs then we
+ * will mitigate softirq work to the softirq thread.
+ */
wakeup_softirqd(cpu);
+ else
+ /*
+ * All softirqs are handled - undo any possible
+ * wakeup of softirqd. This reduces context switch
+ * overhead.
+ */
+ unwakeup_softirqd(cpu);
}

local_irq_restore(flags);
}

-/*
- * This function must run with irq disabled!
- */
-inline void cpu_raise_softirq(unsigned int cpu, unsigned int nr)
-{
- __cpu_raise_softirq(cpu, nr);
-
- /*
- * If we're in an interrupt or bh, we're done
- * (this also catches bh-disabled code). We will
- * actually run the softirq once we return from
- * the irq or bh.
- *
- * Otherwise we wake up ksoftirqd to make sure we
- * schedule the softirq soon.
- */
- if (!(local_irq_count(cpu) | local_bh_count(cpu)))
- wakeup_softirqd(cpu);
-}
-
-void raise_softirq(unsigned int nr)
-{
- long flags;
-
- local_irq_save(flags);
- cpu_raise_softirq(smp_processor_id(), nr);
- local_irq_restore(flags);
-}
-
void open_softirq(int nr, void (*action)(struct softirq_action*), void *data)
{
softirq_vec[nr].data = data;
softirq_vec[nr].action = action;
}

-
/* Tasklets */

struct tasklet_head tasklet_vec[NR_CPUS] __cacheline_aligned;
@@ -157,8 +162,9 @@
local_irq_save(flags);
t->next = tasklet_vec[cpu].list;
tasklet_vec[cpu].list = t;
- cpu_raise_softirq(cpu, TASKLET_SOFTIRQ);
+ __cpu_raise_softirq(cpu, TASKLET_SOFTIRQ);
local_irq_restore(flags);
+ rerun_softirqs(cpu);
}

void __tasklet_hi_schedule(struct tasklet_struct *t)
@@ -169,8 +175,9 @@
local_irq_save(flags);
t->next = tasklet_hi_vec[cpu].list;
tasklet_hi_vec[cpu].list = t;
- cpu_raise_softirq(cpu, HI_SOFTIRQ);
+ __cpu_raise_softirq(cpu, HI_SOFTIRQ);
local_irq_restore(flags);
+ rerun_softirqs(cpu);
}

static void tasklet_action(struct softirq_action *a)
@@ -241,7 +248,6 @@
}
}

-
void tasklet_init(struct tasklet_struct *t,
void (*func)(unsigned long), unsigned long data)
{
@@ -268,8 +274,6 @@
clear_bit(TASKLET_STATE_SCHED, &t->state);
}

-
-
/* Old style BHs */

static void (*bh_base[32])(void);
@@ -325,7 +329,7 @@
{
int i;

- for (i=0; i<32; i++)
+ for (i = 0; i < 32; i++)
tasklet_init(bh_task_vec+i, bh_action, i);

open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
@@ -361,56 +365,52 @@

static int ksoftirqd(void * __bind_cpu)
{
- int bind_cpu = *(int *) __bind_cpu;
- int cpu = cpu_logical_map(bind_cpu);
+ int cpu = cpu_logical_map((int)__bind_cpu);

daemonize();
- current->nice = 19;
+
sigfillset(&current->blocked);

/* Migrate to the right CPU */
- current->cpus_allowed = 1UL << cpu;
- while (smp_processor_id() != cpu)
- schedule();
+ current->cpus_allowed = 1 << cpu;

- sprintf(current->comm, "ksoftirqd_CPU%d", bind_cpu);
+#if CONFIG_SMP
+ sprintf(current->comm, "ksoftirqd CPU%d", cpu);
+#else
+ sprintf(current->comm, "ksoftirqd");
+#endif

+ current->nice = 19;
+ schedule();
__set_current_state(TASK_INTERRUPTIBLE);
- mb();
-
ksoftirqd_task(cpu) = current;

for (;;) {
- if (!softirq_pending(cpu))
- schedule();
-
- __set_current_state(TASK_RUNNING);
-
- while (softirq_pending(cpu)) {
+back:
+ do {
do_softirq();
if (current->need_resched)
- schedule();
- }
-
+ goto preempt;
+ } while (softirq_pending(cpu));
+ schedule();
__set_current_state(TASK_INTERRUPTIBLE);
}
+
+preempt:
+ __set_current_state(TASK_RUNNING);
+ schedule();
+ __set_current_state(TASK_INTERRUPTIBLE);
+ goto back;
}

static __init int spawn_ksoftirqd(void)
{
int cpu;

- for (cpu = 0; cpu < smp_num_cpus; cpu++) {
- if (kernel_thread(ksoftirqd, (void *) &cpu,
+ for (cpu = 0; cpu < smp_num_cpus; cpu++)
+ if (kernel_thread(ksoftirqd, (void *) cpu,
CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0)
- printk("spawn_ksoftirqd() failed for cpu %d\n", cpu);
- else {
- while (!ksoftirqd_task(cpu_logical_map(cpu))) {
- current->policy |= SCHED_YIELD;
- schedule();
- }
- }
- }
+ BUG();

return 0;
}
--- linux/include/linux/netdevice.h.orig Wed Sep 26 17:04:36 2001
+++ linux/include/linux/netdevice.h Wed Sep 26 17:08:20 2001
@@ -486,8 +486,9 @@
local_irq_save(flags);
dev->next_sched = softnet_data[cpu].output_queue;
softnet_data[cpu].output_queue = dev;
- cpu_raise_softirq(cpu, NET_TX_SOFTIRQ);
+ __cpu_raise_softirq(cpu, NET_TX_SOFTIRQ);
local_irq_restore(flags);
+ rerun_softirqs(cpu);
}
}

@@ -535,8 +536,9 @@
local_irq_save(flags);
skb->next = softnet_data[cpu].completion_queue;
softnet_data[cpu].completion_queue = skb;
- cpu_raise_softirq(cpu, NET_TX_SOFTIRQ);
+ __cpu_raise_softirq(cpu, NET_TX_SOFTIRQ);
local_irq_restore(flags);
+ rerun_softirqs(cpu);
}
}

--- linux/include/linux/interrupt.h.orig Wed Sep 26 17:04:40 2001
+++ linux/include/linux/interrupt.h Wed Sep 26 20:57:12 2001
@@ -74,9 +74,14 @@
asmlinkage void do_softirq(void);
extern void open_softirq(int nr, void (*action)(struct softirq_action*), void *data);
extern void softirq_init(void);
-#define __cpu_raise_softirq(cpu, nr) do { softirq_pending(cpu) |= 1UL << (nr); } while (0)
-extern void FASTCALL(cpu_raise_softirq(unsigned int cpu, unsigned int nr));
-extern void FASTCALL(raise_softirq(unsigned int nr));
+#define __cpu_raise_softirq(cpu, nr) \
+ do { softirq_pending(cpu) |= 1UL << (nr); } while (0)
+
+#define rerun_softirqs(cpu) \
+do { \
+ if (!(local_irq_count(cpu) | local_bh_count(cpu))) \
+ do_softirq(); \
+} while (0);



--- linux/include/linux/sched.h.orig Wed Sep 26 17:04:40 2001
+++ linux/include/linux/sched.h Wed Sep 26 17:08:16 2001
@@ -556,6 +556,7 @@

extern void FASTCALL(__wake_up(wait_queue_head_t *q, unsigned int mode, int nr));
extern void FASTCALL(__wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr));
+extern void FASTCALL(__unwakeup_process(struct task_struct * p, long state));
extern void FASTCALL(sleep_on(wait_queue_head_t *q));
extern long FASTCALL(sleep_on_timeout(wait_queue_head_t *q,
signed long timeout));
@@ -574,6 +575,13 @@
#define wake_up_interruptible_all(x) __wake_up((x),TASK_INTERRUPTIBLE, 0)
#define wake_up_interruptible_sync(x) __wake_up_sync((x),TASK_INTERRUPTIBLE, 1)
#define wake_up_interruptible_sync_nr(x) __wake_up_sync((x),TASK_INTERRUPTIBLE, nr)
+
+#define unwakeup_process(tsk,state) \
+do { \
+ if (task_on_runqueue(tsk)) \
+ __unwakeup_process(tsk,state); \
+} while (0)
+
asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struct rusage * ru);

extern int in_group_p(gid_t);
--- linux/include/asm-mips/softirq.h.orig Wed Sep 26 20:58:00 2001
+++ linux/include/asm-mips/softirq.h Wed Sep 26 20:58:07 2001
@@ -40,6 +40,4 @@

#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

-#define __cpu_raise_softirq(cpu, nr) set_bit(nr, &softirq_pending(cpu))
-
#endif /* _ASM_SOFTIRQ_H */
--- linux/include/asm-mips64/softirq.h.orig Wed Sep 26 20:58:20 2001
+++ linux/include/asm-mips64/softirq.h Wed Sep 26 20:58:26 2001
@@ -39,19 +39,4 @@

#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

-extern inline void __cpu_raise_softirq(int cpu, int nr)
-{
- unsigned int *m = (unsigned int *) &softirq_pending(cpu);
- unsigned int temp;
-
- __asm__ __volatile__(
- "1:\tll\t%0, %1\t\t\t# __cpu_raise_softirq\n\t"
- "or\t%0, %2\n\t"
- "sc\t%0, %1\n\t"
- "beqz\t%0, 1b"
- : "=&r" (temp), "=m" (*m)
- : "ir" (1UL << nr), "m" (*m)
- : "memory");
-}
-
#endif /* _ASM_SOFTIRQ_H */
--- linux/net/core/dev.c.orig Wed Sep 26 17:04:41 2001
+++ linux/net/core/dev.c Wed Sep 26 17:04:48 2001
@@ -1218,8 +1218,9 @@
dev_hold(skb->dev);
__skb_queue_tail(&queue->input_pkt_queue,skb);
/* Runs from irqs or BH's, no need to wake BH */
- cpu_raise_softirq(this_cpu, NET_RX_SOFTIRQ);
+ __cpu_raise_softirq(this_cpu, NET_RX_SOFTIRQ);
local_irq_restore(flags);
+ rerun_softirqs(this_cpu);
#ifndef OFFLINE_SAMPLE
get_sample_stats(this_cpu);
#endif
@@ -1529,8 +1530,9 @@
local_irq_disable();
netdev_rx_stat[this_cpu].time_squeeze++;
/* This already runs in BH context, no need to wake up BH's */
- cpu_raise_softirq(this_cpu, NET_RX_SOFTIRQ);
+ __cpu_raise_softirq(this_cpu, NET_RX_SOFTIRQ);
local_irq_enable();
+ rerun_softirqs(this_cpu);

NET_PROFILE_LEAVE(softnet_process);
return;
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