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| author | Chris Wilson <chris@chris-wilson.co.uk> | 2016-07-23 21:27:50 +0300 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2016-09-14 22:57:43 +0300 |
| commit | 12adfd882c5f37548acaba4f043a158b3c54468b (patch) | |
| tree | 83c46e074a1044db2364cd712111550c994c3bc8 | |
| parent | 3563a438f124cb0b8cfd350c86de2f26c63d8837 (diff) | |
| download | linux-12adfd882c5f37548acaba4f043a158b3c54468b.tar.xz | |
list: Expand list_first_entry_or_null()
Due to the use of READ_ONCE() in list_empty() the compiler cannot
optimise !list_empty() ? list_first_entry() : NULL very well. By
manually expanding list_first_entry_or_null() we can take advantage of
the READ_ONCE() to avoid the list element changing under the test while
the compiler can generate smaller code.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Josef Bacik <jbacik@fb.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| -rw-r--r-- | include/linux/list.h | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/include/linux/list.h b/include/linux/list.h index 5183138aa932..5809e9a2de5b 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -381,8 +381,11 @@ static inline void list_splice_tail_init(struct list_head *list, * * Note that if the list is empty, it returns NULL. */ -#define list_first_entry_or_null(ptr, type, member) \ - (!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL) +#define list_first_entry_or_null(ptr, type, member) ({ \ + struct list_head *head__ = (ptr); \ + struct list_head *pos__ = READ_ONCE(head__->next); \ + pos__ != head__ ? list_entry(pos__, type, member) : NULL; \ +}) /** * list_next_entry - get the next element in list |