Re: [PATCH v3] signals: Avoid unnecessary taking of sighand->siglock

[Waiman Long]

On 09/27/2016 12:17 PM, Oleg Nesterov wrote:
> On 09/27, Waiman Long wrote:
> > +static inline int sigequalsets(const sigset_t *set1, const sigset_t *set2)
> > +{
> > +	switch (_NSIG_WORDS) {
> > +	case 4:
> > +		return	(set1->sig[3] == set2->sig[3])&&
> > +			(set1->sig[2] == set2->sig[2])&&
> > +			(set1->sig[1] == set2->sig[1])&&
> > +			(set1->sig[0] == set2->sig[0]);
> > +	case 2:
> > +		return	(set1->sig[1] == set2->sig[1])&&
> > +			(set1->sig[0] == set2->sig[0]);
> > +	case 1:
> > +		return	set1->sig[0] == set2->sig[0];
> > +	}
> > +	return 0;
> > +}
> > +
> OK, this memcmp-by-hand matches other sig* helpers. Well, perhaps
>
> 	default:
> 		BUILD_BUG();
>
> makes sense too, but I won't insist.

We already have a BUILD_BUG() call in sigemptyset(). I don't think we 
need more than one in any given source file. The memcmp() call will be 
more efficient for long byte stream. For short one like sigset_t, direct 
comparison is likely to be faster.

> Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx> 

Thanks for the review.

Cheers,
Longman