linux-kernel - Re: [patch 10/12] sched: remove SYNC

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Message-Id: <1268301817.6785.47.camel@marge.simson.net>
Date:	Thu, 11 Mar 2010 11:03:37 +0100
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 10/12] sched: remove SYNC_WAKEUPS feature


sched: remove SYNC_WAKEUPS feature

Sync wakeups are critical functionality with a long history.  Remove it, we don't
need the branch or icache footprint.

Signed-off-by: Mike Galbraith <efault@....de>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <new-submission>

---
 kernel/sched.c          |    3 ---
 kernel/sched_features.h |    8 --------
 2 files changed, 11 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2369,9 +2369,6 @@ static int try_to_wake_up(struct task_st
 	unsigned long flags;
 	struct rq *rq, *orig_rq;
 
-	if (!sched_feat(SYNC_WAKEUPS))
-		wake_flags &= ~WF_SYNC;
-
 	this_cpu = get_cpu();
 
 	smp_wmb();
Index: linux-2.6/kernel/sched_features.h
===================================================================
--- linux-2.6.orig/kernel/sched_features.h
+++ linux-2.6/kernel/sched_features.h
@@ -17,14 +17,6 @@ SCHED_FEAT(START_DEBIT, 1)
 SCHED_FEAT(WAKEUP_PREEMPT, 1)
 
 /*
- * Use the SYNC wakeup hint, pipes and the likes use this to indicate
- * the remote end is likely to consume the data we just wrote, and
- * therefore has cache benefit from being placed on the same cpu, see
- * also AFFINE_WAKEUPS.
- */
-SCHED_FEAT(SYNC_WAKEUPS, 1)
-
-/*
  * Based on load and program behaviour, see if it makes sense to place
  * a newly woken task on the same cpu as the task that woke it --
  * improve cache locality. Typically used with SYNC wakeups as


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