Re: [patch] fix SMT scheduler latency bug

[Con Kolivas <kernel@kolivas.org>]

On Thu, 23 Jun 2005 10:03, Con Kolivas wrote:
> About the only scenario I can envision a high priority task being delayed
> with the code as it currently is in 2.6.12-mm1 is with a high priority task
> being on the expired array and a low priority task being delayed on the
> active array. This still should not create large latencies unless array
> swapping is significantly delayed. I considered adding a check for this
> originally but it seemed to be unnecessary extra complexity since an
> expired task by design is expected to be delayed more anyway.

BTW if this is an issue it would only require a patch like this.

Cheers,
Con

Index: linux-2.6.12-mm1/kernel/sched.c
===================================================================
--- linux-2.6.12-mm1.orig/kernel/sched.c	2005-06-23 00:10:22.000000000 +1000
+++ linux-2.6.12-mm1/kernel/sched.c	2005-06-23 23:19:35.000000000 +1000
@@ -2784,7 +2784,8 @@ static inline int dependent_sleeper(int 
 					ret = 1;
 		} else
 			if (((smt_curr->time_slice * (100 - sd->per_cpu_gain) /
-				100) > task_timeslice(p)))
+				100) > task_timeslice(p)) &&
+				p->static_prio <= this_rq->best_expired_prio)
 					ret = 1;
 
 check_smt_task:
@@ -2807,7 +2808,8 @@ check_smt_task:
 					resched_task(smt_curr);
 		} else {
 			if ((p->time_slice * (100 - sd->per_cpu_gain) / 100) >
-				task_timeslice(smt_curr))
+				task_timeslice(smt_curr) &&
+				smt_curr->static_prio <= smt_rq->best_expired_prio)
 					resched_task(smt_curr);
 			else
 				wakeup_busy_runqueue(smt_rq);