RE: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled

[David Laight]

From: David Hildenbrand [...
> > This should be likely() instead of unlikely(), no?
> > I'd rather write this
> >
> > 	if (pagefault_disabled())
> >  		return;
> > 	__might_sleep(file, line, 0);
> >
> > and leave the likely stuff completely away.
> 
> Makes perfect sense!

>From my experience of getting (an older version of) gcc to emit
'correctly' statically predicted branches I found that code that
looks like (I don't think return/goto make any difference):

	If (unlikely(condition)) {
		code;
	}
	more_code;

is compile with a forwards conditional branch (ie ignoring the unlikely()).
Similarly 'if () continue' is likely to generate a 'predicted taken'
backwards conditional branch.

To get the desired effect you need a non-empty 'else' part, an assembler
comment will suffice, eg: asm volatile("# comment").

	David



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