[PATCH] 2.5.72 O(1) interactivity bugfix

[Con Kolivas <kernel@kolivas.org>]

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Hi Ingo, all

While messing with the interactivity code I found what appears to be an 
uninitialised variable (p->sleep_avg), which is responsible for all the 
boost/penalty in the scheduler. Initialising this variable to 0 seems to have 
made absolutely massive improvements to system responsiveness under load
and completely removed audio skips up to doing a make -j64 on my uniprocessor 
P4 (beyond which swap starts being used), without changing the scheduler 
timeslices. This seems to help all 2.4 O(1) based kernels as well. Attached 
is a patch against 2.5.72 but I'm not sure about the best place to initialise 
it.


diff -Naurp linux-2.5.72/kernel/fork.c linux-2.5.72-test/kernel/fork.c
- --- linux-2.5.72/kernel/fork.c	2003-06-18 22:47:25.000000000 +1000
+++ linux-2.5.72-test/kernel/fork.c	2003-06-19 00:30:26.000000000 +1000
@@ -864,6 +864,7 @@ struct task_struct *copy_process(unsigne
 	p->lock_depth = -1;		/* -1 = no lock */
 	p->start_time = get_jiffies_64();
 	p->security = NULL;
+	p->sleep_avg = 0;

 	retval = -ENOMEM;
 	if ((retval = security_task_alloc(p)))
diff -Naurp linux-2.5.72/kernel/sched.c linux-2.5.72-test/kernel/sched.c
- --- linux-2.5.72/kernel/sched.c	2003-06-18 22:47:25.000000000 +1000
+++ linux-2.5.72-test/kernel/sched.c	2003-06-19 00:28:19.000000000 +1000
@@ -1755,6 +1755,7 @@ static int setscheduler(pid_t pid, int p
 	if (array)
 		deactivate_task(p, task_rq(p));
 	retval = 0;
+	p->sleep_avg = 0;
 	p->policy = policy;
 	p->rt_priority = lp.sched_priority;
 	if (policy != SCHED_NORMAL)


I hope this is correct.

Regards,
Con
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