Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled | Date | Fri, 5 Dec 2014 12:08:19 +0000 |
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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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