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lib: list_sort.c: Limit number of unused cmp callbacks 

The helper merge_and_restore_back_links() makes sure to call the
caller's cmp function during the final ->prev pointer fixup, so that the
cmp function may call cond_resched().  However, if the cmp function does
not call cond_resched() at all, this is entirely redundant.  If it does,
doing at least two function calls for every two pointer assignments is a
bit excessive.  This patch limits the calls to once for every 256
iterations.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Don Mullis <don.mullis@gmail.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rasmus Villemoes 2014-08-06 16:09:44 -07:00 committed by Linus Torvalds
parent 694123031d
commit 61b3d6c48f
1 changed files with 3 additions and 1 deletions
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4
lib/list_sort.c
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@ -47,6 +47,7 @@ static void merge_and_restore_back_links(void *priv,
struct list_head *a, struct list_head *b)
{
struct list_head *tail = head;
u8 count = 0;
while (a && b) {
/* if equal, take 'a' -- important for sort stability */
@ -70,7 +71,8 @@ static void merge_and_restore_back_links(void *priv,
* element comparison is needed, so the client's cmp()
* routine can invoke cond_resched() periodically.
*/
(*cmp)(priv, tail->next, tail->next);
if (unlikely(!(++count)))
(*cmp)(priv, tail->next, tail->next);
tail->next->prev = tail;
tail = tail->next;