Re: [PATCH] seq_file: Optimize seq_puts()

[Christophe JAILLET]

Le 17/04/2024 à 03:04, Al Viro a écrit :
> On Tue, Apr 16, 2024 at 08:56:51PM +0000, David Laight wrote:
>
> > > static inline void seq_puts(struct seq_file *m, const char *s)
> >
> > That probably needs to be 'always_inline'.
>
> What for?  If compiler fails to inline it (and I'd be very surprised
> if that happened - if s is not a constant string, we get a straight call
> of __seq_puts() and for constant strings it boils down to call of
> seq_putc(m, constant) or seq_write(m, s, constant)), nothing bad
> would happen; we'd still get correct behaviour.
>
> > > {
> > > 	if (!__builtin_constant_p(*s))
> > > 		__seq_puts(m, s);
> > > 	else if (s[0] && !s[1])
> > > 		seq_putc(m, s[0]);
> > > 	else
> > > 		seq_write(m, s, __builtin_strlen(s));
> > > }
> >
> > You missed seq_puts(m, "");
>
> Where have you seen one?

Based on results from:
   git grep seq_puts.*\"\"

there is no such cases.


>  And if it gets less than optimal, who cares?
>
> > Could you do:
> > 	size_t len = __builtin_strlen(s);
> > 	if (!__builtin_constant_p(len))
> > 		__seq_puts(m, s);
> > 	else switch (len){
> > 	case 0: break;
> > 	case 1: seq_putc(m, s[0]);

missing break;

> > 	default: seq_write(m, s, len);
> > 	}
>
> Umm...  That's probably OK, but I wonder how useful would that
> be...

Thanks all for your feedback.

I'll send a v2.

CJ

>