Revert "Revert "ANDROID: sched: avoid migrating when softint on tgt cpu should be short""

This reverts commit 4196c1dafc, as the
merge conflicts have been resolved.

Bug: 31752786
Bug: 168521633
Change-Id: I6cb3fc698d567e03c67e2c4373ce75cc71cdfe9c
Signed-off-by: John Dias <joaodias@google.com>
[elavila: Amend commit text for AOSP, port to mainline]
Signed-off-by: J. Avila <elavila@google.com>
[ashayj@codeaurora.org: update usage of __IRQ_STAT and minor conflicts]
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>
Signed-off-by: Shaleen Agrawal <shalagra@codeaurora.org>

include/linux/interrupt.h

@@ -529,6 +529,12 @@ enum
 };
 
 #define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ))
+/* Softirq's where the handling might be long: */
+#define LONG_SOFTIRQ_MASK ((1 << NET_TX_SOFTIRQ)       | \
+			   (1 << NET_RX_SOFTIRQ)       | \
+			   (1 << BLOCK_SOFTIRQ)        | \
+			   (1 << IRQ_POLL_SOFTIRQ) | \
+			   (1 << TASKLET_SOFTIRQ))
 
 /* map softirq index to softirq name. update 'softirq_to_name' in
  * kernel/softirq.c when adding a new softirq.
@@ -555,6 +561,7 @@ extern void raise_softirq_irqoff(unsigned int nr);
 extern void raise_softirq(unsigned int nr);
 
 DECLARE_PER_CPU(struct task_struct *, ksoftirqd);
+DECLARE_PER_CPU(__u32, active_softirqs);
 
 static inline struct task_struct *this_cpu_ksoftirqd(void)
 {

kernel/sched/rt.c

@@ -1441,15 +1441,20 @@ static int find_lowest_rq(struct task_struct *task);
 #ifdef CONFIG_RT_SOFTINT_OPTIMIZATION
 /*
  * Return whether the task on the given cpu is currently non-preemptible
- * while handling a softirq or is likely to block preemptions soon because
+ * while handling a potentially long softint, or if the task is likely
- * it is a ksoftirq thread.
+ * to block preemptions soon because it is a ksoftirq thread that is
+ * handling slow softints.
  */
 bool
 task_may_not_preempt(struct task_struct *task, int cpu)
 {
+	__u32 softirqs = per_cpu(active_softirqs, cpu) |
+			local_softirq_pending();
+
 	struct task_struct *cpu_ksoftirqd = per_cpu(ksoftirqd, cpu);
-	return (task_thread_info(task)->preempt_count & SOFTIRQ_MASK) ||
+	return ((softirqs & LONG_SOFTIRQ_MASK) &&
-	       task == cpu_ksoftirqd;
+		(task == cpu_ksoftirqd ||
+		 task_thread_info(task)->preempt_count & SOFTIRQ_MASK));
 }
 #endif /* CONFIG_RT_SOFTINT_OPTIMIZATION */
 

kernel/softirq.c

@@ -63,6 +63,13 @@ static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp
 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
 EXPORT_PER_CPU_SYMBOL_GPL(ksoftirqd);
 
+/*
+ * active_softirqs -- per cpu, a mask of softirqs that are being handled,
+ * with the expectation that approximate answers are acceptable and therefore
+ * no synchronization.
+ */
+DEFINE_PER_CPU(__u32, active_softirqs);
+
 const char * const softirq_to_name[NR_SOFTIRQS] = {
 	"HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
 	"TASKLET", "SCHED", "HRTIMER", "RCU"
@@ -541,6 +548,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 restart:
 	/* Reset the pending bitmask before enabling irqs */
 	set_softirq_pending(0);
+	__this_cpu_write(active_softirqs, pending);
 
 	local_irq_enable();
 
@@ -570,6 +578,7 @@ restart:
 		pending >>= softirq_bit;
 	}
 
+	__this_cpu_write(active_softirqs, 0);
 	if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
 	    __this_cpu_read(ksoftirqd) == current)
 		rcu_softirq_qs();