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Message-Id: <20080920.035602.226564809.davem@davemloft.net>
Date: Sat, 20 Sep 2008 03:56:02 -0700 (PDT)
From: David Miller <davem@...emloft.net>
To: akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
jens.axboe@...cle.com, steffen.klassert@...unet.com
Subject: Re: [PATCH 2/2]: softirq: Add support for triggering softirq work
on softirqs.
From: Andrew Morton <akpm@...ux-foundation.org>
Date: Sat, 20 Sep 2008 00:46:08 -0700
> Took a little staring to work out what that test is doing. Adding
>
> /* If the list was previouly empty, trigger a softirq run */
>
> would be nice.
Ok.
> CONFIG_USE_GENERIC_SMP_HELPERS=y, CONFIG_SMP=n shouldn't be possible,
> if we care..
Sure.
> OK, now what's going on with call_single_data.flags?
I've split flags into "priv" and "flags" u16's.
> Is locking needed to keep that CPU online after this test?
You already know :)
> Ah. So it is required that the __send_remote_softirq() caller disable
> local interrupts. There's my locking. It's worth a mention in the
> interface description, if not a WARN_ON().
Fair enough.
> It's best to provide some documentation for global, exported-to-modules
> functions please.
I've got your kerneldoc right here buddy boy...
> Could use __local_trigger() here I think, although that wouldn't really
> improve anything much.
This is a splice, so we'd need to iterate which would be cumbersome
and error prone.
Here is the updated patch.
softirq: Add support for triggering softirq work on softirqs.
This is basically a genericization of Jens Axboe's block layer
remote softirq changes.
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
---
include/linux/interrupt.h | 13 +++++
include/linux/smp.h | 4 +-
kernel/softirq.c | 128 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 144 insertions(+), 1 deletions(-)
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index fdd7b90..d8713c7 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -11,6 +11,8 @@
#include <linux/hardirq.h>
#include <linux/sched.h>
#include <linux/irqflags.h>
+#include <linux/smp.h>
+#include <linux/percpu.h>
#include <asm/atomic.h>
#include <asm/ptrace.h>
#include <asm/system.h>
@@ -271,7 +273,18 @@ 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);
+DECLARE_PER_CPU(struct list_head, softirq_work_list[NR_SOFTIRQ]);
+/* Try to send a softirq to a remote cpu. If this cannot be done, the
+ * work will be queued to the local cpu.
+ */
+extern void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq);
+
+/* Like send_remote_softirq(), but the caller must disable local cpu interrupts
+ * and compute the current cpu, passed in as 'this_cpu'.
+ */
+extern void __send_remote_softirq(struct call_single_data *cp, int cpu,
+ int this_cpu, int softirq);
/* Tasklets --- multithreaded analogue of BHs.
diff --git a/include/linux/smp.h b/include/linux/smp.h
index 66484d4..2e4d58b 100644
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -7,6 +7,7 @@
*/
#include <linux/errno.h>
+#include <linux/types.h>
#include <linux/list.h>
#include <linux/cpumask.h>
@@ -16,7 +17,8 @@ struct call_single_data {
struct list_head list;
void (*func) (void *info);
void *info;
- unsigned int flags;
+ u16 flags;
+ u16 priv;
};
#ifdef CONFIG_SMP
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 27642a2..6c7b226 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -6,6 +6,8 @@
* Distribute under GPLv2.
*
* Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
+ *
+ * Remote softirq infrastructure is by Jens Axboe.
*/
#include <linux/module.h>
@@ -463,17 +465,143 @@ void tasklet_kill(struct tasklet_struct *t)
EXPORT_SYMBOL(tasklet_kill);
+DEFINE_PER_CPU(struct list_head, softirq_work_list[NR_SOFTIRQ]);
+
+static void __local_trigger(struct call_single_data *cp, int softirq)
+{
+ struct list_head *head = &__get_cpu_var(softirq_work_list[softirq]);
+
+ list_add_tail(&cp->list, head);
+
+ /* Trigger the softirq only if the list was previously empty. */
+ if (head->next == &cp->list)
+ raise_softirq_irqoff(softirq);
+}
+
+#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
+static void remote_softirq_receive(void *data)
+{
+ struct call_single_data *cp = data;
+ unsigned long flags;
+ int softirq;
+
+ softirq = cp->priv;
+
+ local_irq_save(flags);
+ __local_trigger(cp, softirq);
+ local_irq_restore(flags);
+}
+
+static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+{
+ if (cpu_online(cpu)) {
+ cp->func = remote_softirq_receive;
+ cp->info = cp;
+ cp->flags = 0;
+ cp->priv = softirq;
+
+ __smp_call_function_single(cpu, cp);
+ return 0;
+ }
+ return 1;
+}
+#else /* CONFIG_USE_GENERIC_SMP_HELPERS */
+static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+{
+ return 1;
+}
+#endif
+
+/***
+ * __send_remote_softirq - try to schedule softirq work on a remote cpu
+ * @cp: private SMP call function data area
+ * @cpu: the remote cpu
+ * @this_cpu: the currently executing cpu
+ * @softirq: the softirq for the work
+ *
+ * Attempt to schedule softirq work on a remote cpu. If this cannot be
+ * done, the work is instead queued up on the local cpu.
+ *
+ * Interrupts must be disabled.
+ */
+void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu, int softirq)
+{
+ if (cpu == this_cpu || __try_remote_softirq(cp, cpu, softirq))
+ __local_trigger(cp, softirq);
+}
+EXPORT_SYMBOL(__send_remote_softirq);
+
+/***
+ * send_remote_softirq - try to schedule softirq work on a remote cpu
+ * @cp: private SMP call function data area
+ * @cpu: the remote cpu
+ * @softirq: the softirq for the work
+ *
+ * Like __send_remote_softirq except that disabling interrupts and
+ * computing the current cpu is done for the caller.
+ */
+void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+{
+ unsigned long flags;
+ int this_cpu;
+
+ local_irq_save(flags);
+ this_cpu = smp_processor_id();
+ __send_remote_softirq(cp, cpu, this_cpu, softirq);
+ local_irq_restore(flags);
+}
+EXPORT_SYMBOL(send_remote_softirq);
+
+static int __cpuinit remote_softirq_cpu_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ /*
+ * If a CPU goes away, splice its entries to the current CPU
+ * and trigger a run of the softirq
+ */
+ if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
+ int cpu = (unsigned long) hcpu;
+ int i;
+
+ local_irq_disable();
+ for (i = 0; i < NR_SOFTIRQ; i++) {
+ struct list_head *head = &per_cpu(softirq_work_list[i], cpu);
+ struct list_head *local_head;
+
+ if (list_empty(head))
+ continue;
+
+ local_head = &__get_cpu_var(softirq_work_list[i]);
+ list_splice_init(head, local_head);
+ raise_softirq_irqoff(i);
+ }
+ local_irq_enable();
+ }
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata remote_softirq_cpu_notifier = {
+ .notifier_call = remote_softirq_cpu_notify,
+};
+
void __init softirq_init(void)
{
int cpu;
for_each_possible_cpu(cpu) {
+ int i;
+
per_cpu(tasklet_vec, cpu).tail =
&per_cpu(tasklet_vec, cpu).head;
per_cpu(tasklet_hi_vec, cpu).tail =
&per_cpu(tasklet_hi_vec, cpu).head;
+ for (i = 0; i < NR_SOFTIRQ; i++)
+ INIT_LIST_HEAD(&per_cpu(softirq_work_list[i], cpu));
}
+ register_hotcpu_notifier(&remote_softirq_cpu_notifier);
+
open_softirq(TASKLET_SOFTIRQ, tasklet_action);
open_softirq(HI_SOFTIRQ, tasklet_hi_action);
}
--
1.5.6.5
--
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