Re: [PATCH RFC] smt nice introduces significant lock contention

[Nick Piggin <nickpiggin@yahoo.com.au>]

Con Kolivas wrote:

> > Nice to acknowledge Chris's idea for 
> > trylocks in your changelog when you submit a final patch.
>
>
> I absolutely would and I would ask for him to sign off on it as well, once we 
> agreed on a final form.

No worries, I thought you would ;)

This is a small micro-optimisation / cleanup we can do after
smtnice gets converted to use trylocks. Might result in a little
less cacheline footprint in some cases.

--
SUSE Labs, Novell Inc.

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c	2006-06-02 17:46:23.000000000 +1000
+++ linux-2.6/kernel/sched.c	2006-06-02 17:48:50.000000000 +1000
@@ -239,7 +239,6 @@ struct runqueue {
 
 	task_t *migration_thread;
 	struct list_head migration_queue;
-	int cpu;
 #endif
 
 #ifdef CONFIG_SCHEDSTATS
@@ -1700,7 +1699,7 @@ static void double_rq_lock(runqueue_t *r
 		spin_lock(&rq1->lock);
 		__acquire(rq2->lock);	/* Fake it out ;) */
 	} else {
-		if (rq1->cpu < rq2->cpu) {
+		if (rq1 < rq2) {
 			spin_lock(&rq1->lock);
 			spin_lock(&rq2->lock);
 		} else {
@@ -1736,7 +1735,7 @@ static void double_lock_balance(runqueue
 	__acquires(this_rq->lock)
 {
 	if (unlikely(!spin_trylock(&busiest->lock))) {
-		if (busiest->cpu < this_rq->cpu) {
+		if (busiest < this_rq) {
 			spin_unlock(&this_rq->lock);
 			spin_lock(&busiest->lock);
 			spin_lock(&this_rq->lock);
@@ -6104,7 +6103,6 @@ void __init sched_init(void)
 		rq->push_cpu = 0;
 		rq->migration_thread = NULL;
 		INIT_LIST_HEAD(&rq->migration_queue);
-		rq->cpu = i;
 #endif
 		atomic_set(&rq->nr_iowait, 0);