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softirq: use ffs() in __do_softirq()

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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>
This commit is contained in:
Joe Perches 2014-01-27 17:07:14 -08:00 committed by Linus Torvalds
parent a19428e5c3
commit 2e702b9f6c
1 changed files with 20 additions and 19 deletions
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39
kernel/softirq.c
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@ -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();
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();