From 2e702b9f6cba4eb87d90e2a2d425a1fc05eec803 Mon Sep 17 00:00:00 2001 From: Joe Perches Date: Mon, 27 Jan 2014 17:07:14 -0800 Subject: [PATCH] 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: Joe Perches Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/softirq.c | 43 ++++++++++++++++++++++--------------------- 1 file changed, 22 insertions(+), 21 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 8a1e6e104892..ba79bbfe380e 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -229,6 +229,7 @@ asmlinkage void __do_softirq(void) struct softirq_action *h; bool in_hardirq; __u32 pending; + int softirq_bit; int cpu; /* @@ -253,30 +254,30 @@ asmlinkage void __do_softirq(void) h = softirq_vec; - do { - if (pending & 1) { - unsigned int vec_nr = h - softirq_vec; - int prev_count = preempt_count(); - - kstat_incr_softirqs_this_cpu(vec_nr); - - trace_softirq_entry(vec_nr); - 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, - prev_count, preempt_count()); - preempt_count_set(prev_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(); - rcu_bh_qs(cpu); + kstat_incr_softirqs_this_cpu(vec_nr); + + trace_softirq_entry(vec_nr); + 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, + prev_count, preempt_count()); + preempt_count_set(prev_count); } + rcu_bh_qs(cpu); h++; - pending >>= 1; - } while (pending); + pending >>= softirq_bit; + } local_irq_disable(); -- GitLab