Re: [PATCH] locking/lockdep: unlikely bfs error check

[Waiman Long]

On 6/16/21 10:59 AM, Xiongwei Song wrote:
> > On Jun 16, 2021, at 10:48 PM, Waiman Long <llong@xxxxxxxxxx> wrote:
> >
> > On 6/16/21 10:42 AM, Xiongwei Song wrote:
> > > From: Xiongwei Song <sxwjean@xxxxxxxxx>
> > >
> > > The error from graph walk is small probability event, so unlikely
> > > bfs_error can improve performance a little bit.
> > >
> > > Signed-off-by: Xiongwei Song <sxwjean@xxxxxxxxx>
> > > ---
> > >   kernel/locking/lockdep.c | 12 ++++++------
> > >   1 file changed, 6 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> > > index 074fd6418c20..af8c9203cd3e 100644
> > > --- a/kernel/locking/lockdep.c
> > > +++ b/kernel/locking/lockdep.c
> > > @@ -2646,7 +2646,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
> > >   	bfs_init_rootb(&this, prev);
> > >     	ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, usage_skip, NULL);
> > > -	if (bfs_error(ret)) {
> > > +	if (unlikely(bfs_error(ret))) {
> > >   		print_bfs_bug(ret);
> > >   		return 0;
> > >   	}
> > > @@ -2664,7 +2664,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
> > >   	bfs_init_root(&that, next);
> > >     	ret = find_usage_forwards(&that, forward_mask, &target_entry1);
> > > -	if (bfs_error(ret)) {
> > > +	if (unlikely(bfs_error(ret))) {
> > >   		print_bfs_bug(ret);
> > >   		return 0;
> > >   	}
> > > @@ -2679,7 +2679,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
> > >   	backward_mask = original_mask(target_entry1->class->usage_mask);
> > >     	ret = find_usage_backwards(&this, backward_mask, &target_entry);
> > > -	if (bfs_error(ret)) {
> > > +	if (unlikely(bfs_error(ret))) {
> > >   		print_bfs_bug(ret);
> > >   		return 0;
> > >   	}
> > > @@ -2998,7 +2998,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
> > >   	 * Is the <prev> -> <next> link redundant?
> > >   	 */
> > >   	ret = check_redundant(prev, next);
> > > -	if (bfs_error(ret))
> > > +	if (unlikely(bfs_error(ret)))
> > >   		return 0;
> > >   	else if (ret == BFS_RMATCH)
> > >   		return 2;
> > > @@ -3911,7 +3911,7 @@ check_usage_forwards(struct task_struct *curr, struct held_lock *this,
> > >     	bfs_init_root(&root, this);
> > >   	ret = find_usage_forwards(&root, usage_mask, &target_entry);
> > > -	if (bfs_error(ret)) {
> > > +	if (unlikely(bfs_error(ret))) {
> > >   		print_bfs_bug(ret);
> > >   		return 0;
> > >   	}
> > > @@ -3946,7 +3946,7 @@ check_usage_backwards(struct task_struct *curr, struct held_lock *this,
> > >     	bfs_init_rootb(&root, this);
> > >   	ret = find_usage_backwards(&root, usage_mask, &target_entry);
> > > -	if (bfs_error(ret)) {
> > > +	if (unlikely(bfs_error(ret))) {
> > >   		print_bfs_bug(ret);
> > >   		return 0;
> > >   	}
> > I think it is better to put the unlikely() directly into the bfs_error() inline function instead of sprinkling it all over the place.
> Sounds good. Thank you for the suggestion. I will update the patch.

Another nit. It is a bit odd that sent out two patches separately though 
they do seem to have a bit of dependency. I think you should post them 
as a 2-patch series.

Cheers,
Longman