From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753226AbaFXKHI (ORCPT ); Tue, 24 Jun 2014 06:07:08 -0400 Received: from mail-lb0-f173.google.com ([209.85.217.173]:59156 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753060AbaFXKHE (ORCPT ); Tue, 24 Jun 2014 06:07:04 -0400 From: Rasmus Villemoes To: Artem Bityutskiy , Don Mullis , Dave Chinner Cc: linux-kernel@vger.kernel.org, Rasmus Villemoes Subject: [PATCH v2 4/4] lib: list_sort.c: Limit number of unused cmp callbacks Date: Tue, 24 Jun 2014 12:06:31 +0200 Message-Id: <1403604392-23259-5-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <1403604392-23259-1-git-send-email-linux@rasmusvillemoes.dk> References: <1403604392-23259-1-git-send-email-linux@rasmusvillemoes.dk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- lib/list_sort.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/lib/list_sort.c b/lib/list_sort.c index a34c78c..6b9fdaf 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; -- 1.9.2