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Commit a66b3eb5 authored by Pavankumar Kondeti's avatar Pavankumar Kondeti
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softirq: defer softirq processing to ksoftirqd if CPU is busy with RT 



Defer the softirq processing to ksoftirqd if a RT task is running
or queued on the current CPU. This complements the RT task placement
algorithm which tries to find a CPU that is not currently busy with
softirqs.

Currently NET_TX, NET_RX, BLOCK and TASKLET softirqs are only deferred
as they can potentially run for long time.

Change-Id: Id7665244af6bbd5a96d9e591cf26154e9eaa860c
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent ca652b3d

include/linux/sched.h

+5 −0
Original line number Diff line number Diff line
@@ -2481,6 +2481,7 @@ extern void do_set_cpus_allowed(struct task_struct *p, 


extern int set_cpus_allowed_ptr(struct task_struct *p,

				const struct cpumask *new_mask);

extern bool cpupri_check_rt(void);

#else

static inline void do_set_cpus_allowed(struct task_struct *p,

				      const struct cpumask *new_mask)
@@ -2493,6 +2494,10 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p, 
		return -EINVAL;

	return 0;

}

static inline bool cpupri_check_rt(void)

{

	return false;

}

#endif



struct sched_load {

kernel/sched/cpupri.c

+11 −0
Original line number Diff line number Diff line
@@ -279,3 +279,14 @@ void cpupri_cleanup(struct cpupri *cp) 
	for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)

		free_cpumask_var(cp->pri_to_cpu[i].mask);

}



/*

 * cpupri_check_rt - check if CPU has a RT task

 * should be called from rcu-sched read section.

 */

bool cpupri_check_rt(void)

{

	int cpu = raw_smp_processor_id();



	return cpu_rq(cpu)->rd->cpupri.cpu_to_pri[cpu] > CPUPRI_NORMAL;

}

kernel/softirq.c

+4 −1
Original line number Diff line number Diff line
@@ -234,6 +234,8 @@ static inline bool lockdep_softirq_start(void) { return false; } 
static inline void lockdep_softirq_end(bool in_hardirq) { }

#endif



#define long_softirq_pending()	(local_softirq_pending() & LONG_SOFTIRQ_MASK)

#define defer_for_rt()		(long_softirq_pending() && cpupri_check_rt())

asmlinkage __visible void __do_softirq(void)

{

	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
@@ -297,6 +299,7 @@ restart: 
	pending = local_softirq_pending();

	if (pending) {

		if (time_before(jiffies, end) && !need_resched() &&

		    !defer_for_rt() &&

		    --max_restart)

			goto restart;
@@ -349,7 +352,7 @@ void irq_enter(void) 


static inline void invoke_softirq(void)

{

	if (!force_irqthreads) {

	if (!force_irqthreads && !defer_for_rt()) {

#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK

		/*

		 * We can safely execute softirq on the current stack if