From kernel@kolivas.org Thu Mar 22 13:04:57 2007 From: Con Kolivas X-KMail-Identity: 2041502994 To: Jeffrey Hundstad Subject: [PATCH] sched: rsdl check for niced tasks lowering prio level Date: Thu, 22 Mar 2007 13:04:57 +1100 User-Agent: KMail/1.9.5 Cc: Artur Skawina , linux list , ck list , Ingo Molnar , Andrew Morton References: <200703220429.45311.kernel@kolivas.org> <200703221124.59126.kernel@kolivas.org> <200703221152.45141.kernel@kolivas.org> In-Reply-To: <200703221152.45141.kernel@kolivas.org> X-KMail-Link-Message: 32042 X-KMail-Link-Type: reply MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200703221304.58011.kernel@kolivas.org> X-KMail-EncryptionState: X-KMail-SignatureState: X-KMail-MDN-Sent: X-Length: 4388 X-UID: 5508 Here is the best fix for the bug pointed out. Thanks. I'll try and find pc time to wrap these two patches together and make a v0.32 available. --- Ensure niced tasks are not inappropriately limiting sleeping unniced tasks by explicitly checking what the best static priority that has run this major rotation was. Reimplement SCHED_BATCH using this check. Signed-off-by: Con Kolivas --- kernel/sched.c | 33 ++++++++++++++++++++++++--------- 1 file changed, 24 insertions(+), 9 deletions(-) Index: linux-2.6.21-rc4-mm1/kernel/sched.c =================================================================== --- linux-2.6.21-rc4-mm1.orig/kernel/sched.c 2007-03-22 12:44:05.000000000 +1100 +++ linux-2.6.21-rc4-mm1/kernel/sched.c 2007-03-22 12:58:26.000000000 +1100 @@ -201,8 +201,11 @@ struct rq { struct prio_array *active, *expired, arrays[2]; unsigned long *dyn_bitmap, *exp_bitmap; - int prio_level; - /* The current dynamic priority level this runqueue is at */ + int prio_level, best_static_prio; + /* + * The current dynamic priority level this runqueue is at, and the + * best static priority queued this major rotation. + */ unsigned long prio_rotation; /* How many times we have rotated the priority queue */ @@ -704,16 +707,24 @@ static inline int entitled_slot(int stat /* * Find the first unused slot by this task that is also in its prio_matrix - * level. + * level. Ensure that the prio_level is not unnecessarily low by checking + * that best_static_prio this major rotation was not a niced task. + * SCHED_BATCH tasks do not perform this check so they do not induce + * latencies in tasks of any nice level. */ static inline int next_entitled_slot(struct task_struct *p, struct rq *rq) { - DECLARE_BITMAP(tmp, PRIO_RANGE); + if (p->static_prio < rq->best_static_prio && p->policy != SCHED_BATCH) + return SCHED_PRIO(find_first_zero_bit(p->bitmap, PRIO_RANGE)); + else { + DECLARE_BITMAP(tmp, PRIO_RANGE); - bitmap_or(tmp, p->bitmap, prio_matrix[USER_PRIO(p->static_prio)], - PRIO_RANGE); - return SCHED_PRIO(find_next_zero_bit(tmp, PRIO_RANGE, - USER_PRIO(rq->prio_level))); + bitmap_or(tmp, p->bitmap, + prio_matrix[USER_PRIO(p->static_prio)], + PRIO_RANGE); + return SCHED_PRIO(find_next_zero_bit(tmp, PRIO_RANGE, + USER_PRIO(rq->prio_level))); + } } static void queue_expired(struct task_struct *p, struct rq *rq) @@ -3315,6 +3326,7 @@ static inline void major_prio_rotation(s rq->active = new_array; rq->exp_bitmap = rq->expired->prio_bitmap; rq->dyn_bitmap = rq->active->prio_bitmap; + rq->best_static_prio = MAX_PRIO; rq->prio_rotation++; } @@ -3640,10 +3652,12 @@ need_resched_nonpreemptible: } switch_tasks: if (next == rq->idle) { + rq->best_static_prio = MAX_PRIO; rq->prio_level = MAX_RT_PRIO; rq->prio_rotation++; schedstat_inc(rq, sched_goidle); - } + } else if (next->static_prio < rq->best_static_prio) + rq->best_static_prio = next->static_prio; prefetch(next); prefetch_stack(next); clear_tsk_need_resched(prev); @@ -7093,6 +7107,7 @@ void __init sched_init(void) lockdep_set_class(&rq->lock, &rq->rq_lock_key); rq->nr_running = 0; rq->prio_rotation = 0; + rq->best_static_prio = MAX_PRIO; rq->prio_level = MAX_RT_PRIO; rq->active = rq->arrays; rq->expired = rq->arrays + 1; -- -ck