Re: [RFC][PATCH 3/3] ipc/sem: Rework wakeup scheme

Peter Zijlstra
2011-09-16T12:39:55Z

On Fri, 2011-09-16 at 14:18 +0200, Peter Zijlstra wrote:
> Currently the wake-list is a FILO, although making it FIFO isn't really
> hard (in fact, I've got the patch).

might as well post it too

---
Subject:
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Thu Sep 15 15:32:06 CEST 2011

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-mus5f94zr5rckytoysdn4pqd@git.kernel.org
---
include/linux/sched.h | 11 ++++++++---
ipc/sem.c | 11 +++++++++--
2 files changed, 17 insertions(+), 5 deletions(-)
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1067,6 +1067,7 @@ struct sched_domain;

struct wake_list_head {
struct wake_list_node *first;
+ struct wake_list_node *last;
};

struct wake_list_node {
@@ -1076,7 +1077,7 @@ struct wake_list_node {
#define WAKE_LIST_TAIL ((struct wake_list_node *)0x01)

#define WAKE_LIST(name) \
- struct wake_list_head name = { WAKE_LIST_TAIL }
+ struct wake_list_head name = { WAKE_LIST_TAIL, WAKE_LIST_TAIL }

/*
* wake flags
@@ -2174,11 +2175,15 @@ wake_list_add(struct wake_list_head *hea
* This cmpxchg() implies a full barrier, which pairs with the write
* barrier implied by the wakeup in wake_up_list().
*/
- if (cmpxchg(&n->next, 0, head->first))
+ if (cmpxchg(&n->next, 0, WAKE_LIST_TAIL))
return;

get_task_struct(p);
- head->first = n;
+ if (head->first == WAKE_LIST_TAIL)
+ head->first = n;
+ else
+ head->last->next = n;
+ head->last = n;
}

extern void wake_up_list(struct wake_list_head *head, unsigned int state);