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authorRasmus Villemoes <linux@rasmusvillemoes.dk>2014-08-06 16:09:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-06 18:01:25 -0700
commit61b3d6c48f059bb054b0019088736dab6c2ac0ec (patch)
tree0d312d70673c63c8e02fcdd7c690e0e67e57922f /lib
parent694123031d12458a343492528fa40113e5ec843e (diff)
downloadlinux-61b3d6c48f059bb054b0019088736dab6c2ac0ec.tar.bz2
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>
Diffstat (limited to 'lib')
-rw-r--r--lib/list_sort.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/lib/list_sort.c b/lib/list_sort.c
index a34c78c30d56..6b9fdaf1d32e 100644
--- a/lib/list_sort.c
+++ b/lib/list_sort.c
@@ -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;