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 <joe@perches.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 8a1e6e1..ba79bbf 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -229,6 +229,7 @@
struct softirq_action *h;
bool in_hardirq;
__u32 pending;
+ int softirq_bit;
int cpu;
/*
@@ -253,30 +254,30 @@
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;
- kstat_incr_softirqs_this_cpu(vec_nr);
+ h += softirq_bit - 1;
- 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);
- }
+ 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();