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Commit 2e702b9f authored by Joe Perches's avatar Joe Perches Committed by Linus Torvalds
Browse files

softirq: use ffs() in __do_softirq() 



Possible speed improvement of __do_softirq() by using ffs() instead of
using a while loop with an & 1 test then single bit shift.

Signed-off-by: default avatarJoe Perches <joe@perches.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a19428e5

kernel/softirq.c

+22 −21
Original line number Diff line number Diff line
@@ -229,6 +229,7 @@ asmlinkage void __do_softirq(void) 
	struct softirq_action *h;

	bool in_hardirq;

	__u32 pending;

	int softirq_bit;

	int cpu;



	/*
@@ -253,10 +254,14 @@ asmlinkage void __do_softirq(void) 


	h = softirq_vec;



	do {

		if (pending & 1) {

			unsigned int vec_nr = h - softirq_vec;

			int prev_count = preempt_count();

	while ((softirq_bit = ffs(pending))) {

		unsigned int vec_nr;

		int prev_count;



		h += softirq_bit - 1;



		vec_nr = h - softirq_vec;

		prev_count = preempt_count();



		kstat_incr_softirqs_this_cpu(vec_nr);
@@ -264,19 +269,15 @@ asmlinkage void __do_softirq(void) 
		h->action(h);

		trace_softirq_exit(vec_nr);

		if (unlikely(prev_count != preempt_count())) {

				printk(KERN_ERR "huh, entered softirq %u %s %p"

				       "with preempt_count %08x,"

				       " exited with %08x?\n", vec_nr,

				       softirq_to_name[vec_nr], h->action,

			printk(KERN_ERR "huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",

			       vec_nr, softirq_to_name[vec_nr], h->action,

			       prev_count, preempt_count());

			preempt_count_set(prev_count);

		}



		rcu_bh_qs(cpu);

		}

		h++;

		pending >>= 1;

	} while (pending);

		pending >>= softirq_bit;

	}



	local_irq_disable();