Normally softirqs are invoked when exiting irqs. When polling in the
cpuidle driver there may be no irq. Therefore pending softirqs go
unnoticed and polling continues without invoking them.
Add a softirq_poll() function to explicitly check for and invoke
softirqs.
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
This commit is not needed for virtio-blk. I added it when I realized
virtio-net's NAPI scheduling might not be detected by the cpuidle busy
wait loop because it is unaware of softirqs. However, even after doing
this virtio-net's NAPI polling doesn't combine with cpuidle haltpoll.
Perhaps this patch is still desirable for cpuidle poll_state in case a
softirq is raised?
---
include/linux/interrupt.h | 2 ++
drivers/cpuidle/poll_source.c | 3 +++
kernel/softirq.c | 14 ++++++++++++++
3 files changed, 19 insertions(+)
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 4777850a6dc7..9bfdcc466ba8 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -573,6 +573,8 @@ struct softirq_action
asmlinkage void do_softirq(void);
asmlinkage void __do_softirq(void);
+extern void softirq_poll(void);
+
extern void open_softirq(int nr, void (*action)(struct softirq_action *));
extern void softirq_init(void);
extern void __raise_softirq_irqoff(unsigned int nr);
diff --git a/drivers/cpuidle/poll_source.c b/drivers/cpuidle/poll_source.c
index 46100e5a71e4..ed200feb0daa 100644
--- a/drivers/cpuidle/poll_source.c
+++ b/drivers/cpuidle/poll_source.c
@@ -6,6 +6,7 @@
#include <linux/lockdep.h>
#include <linux/percpu.h>
#include <linux/poll_source.h>
+#include <linux/interrupt.h>
/* The per-cpu list of registered poll sources */
DEFINE_PER_CPU(struct list_head, poll_source_list);
@@ -26,6 +27,8 @@ void poll_source_run_once(void)
list_for_each_entry(src, this_cpu_ptr(&poll_source_list), node)
src->ops->poll(src);
+
+ softirq_poll();
}
/* Called from idle task with TIF_POLLING_NRFLAG set and irqs enabled */
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 4992853ef53d..f45bf0204218 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -611,6 +611,20 @@ void irq_enter(void)
irq_enter_rcu();
}
+/**
+ * softirq_poll() - invoke pending softirqs
+ *
+ * Normally it is not necessary to explicitly poll for softirqs, but in the
+ * cpuidle driver a polling function may have raised a softirq with no irq exit
+ * to invoke it. Therefore it is necessary to poll for pending softirqs and
+ * invoke them explicitly.
+ */
+void softirq_poll(void)
+{
+ if (!in_interrupt() && local_softirq_pending())
+ invoke_softirq();
+}
+
static inline void tick_irq_exit(void)
{
#ifdef CONFIG_NO_HZ_COMMON
--
2.31.1
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