Re: [PATCH] kernel/softirq.c: delete 'while' looping to improve a little performance and beautify code

[Chen Gang <gang.chen@asianux.com>]

On 06/10/2013 08:25 PM, Paul E. McKenney wrote:
> On Sun, Jun 09, 2013 at 08:30:19PM +0800, Chen Gang wrote:
>> > 
>> > After finish the internal 'while', need not test TASKLET_STATE_SCHED
>> > again, so looping back to outside 'while' is only for set_bit().
>> > 
>> > When use 'if' and set_bit() instead of 'while', it will save at least
>> > one running conditional instruction, and also will be clearer for readers
>> > (although the binary size will be a little bigger).
>> > 
>> > The related patch is "1da177e Linux-2.6.12-rc2"
>> > 
>> > 
>> > Signed-off-by: Chen Gang <gang.chen@asianux.com>
>> > ---
>> >  kernel/softirq.c |    3 ++-
>> >  1 files changed, 2 insertions(+), 1 deletions(-)
>> > 
>> > diff --git a/kernel/softirq.c b/kernel/softirq.c
>> > index a5f8836..52da25f 100644
>> > --- a/kernel/softirq.c
>> > +++ b/kernel/softirq.c
>> > @@ -540,10 +540,11 @@ void tasklet_kill(struct tasklet_struct *t)
>> >  	if (in_interrupt())
>> >  		printk("Attempt to kill tasklet from interrupt\n");
>> > 
>> > -	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
>> > +	if (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
>> >  		do {
>> >  			yield();
>> >  		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
>> > +		set_bit(TASKLET_STATE_SCHED, &t->state);
> This replaces an atomic test-and-set with two operations, a test and
> a set.  Is this safe?

Oh, it seems not safe, at least it is not the original author's willing.

It is my fault, and also sorry for replying late.


Thanks.
-- 
Chen Gang

Asianux Corporation