Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751300AbWCRFGU (ORCPT ); Sat, 18 Mar 2006 00:06:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751421AbWCRFGU (ORCPT ); Sat, 18 Mar 2006 00:06:20 -0500 Received: from mail.gmx.net ([213.165.64.20]:48837 "HELO mail.gmx.net") by vger.kernel.org with SMTP id S1751300AbWCRFGT (ORCPT ); Sat, 18 Mar 2006 00:06:19 -0500 X-Authenticated: #14349625 Subject: [2.6.16-rc6 patch] fix interactive task starvation From: Mike Galbraith To: lkml Cc: Ingo Molnar , Andrew Morton Content-Type: text/plain Date: Sat, 18 Mar 2006 06:08:00 +0100 Message-Id: <1142658480.8262.38.camel@homer> Mime-Version: 1.0 X-Mailer: Evolution 2.4.0 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2895 Lines: 80 Greetings, The patch below fixes a starvation problem that occurs when a stream of highly interactive tasks delay an array switch for extended periods despite EXPIRED_STARVING(rq) being true. AFAIKT, the only choice is to enqueue awakening tasks on the expired array in this case. Without this patch, it can be nearly impossible to remotely login to a busy server, and interactive shell commands can starve for minutes. This has not been verified by anyone. Comments? -Mike Signed-off-by: Mike Galbraith --- linux-2.6.16-rc6/kernel/sched.c.org 2006-03-17 14:48:35.000000000 +0100 +++ linux-2.6.16-rc6/kernel/sched.c 2006-03-17 17:41:25.000000000 +0100 @@ -662,11 +662,30 @@ } /* + * We place interactive tasks back into the active array, if possible. + * + * To guarantee that this does not starve expired tasks we ignore the + * interactivity of a task if the first expired task had to wait more + * than a 'reasonable' amount of time. This deadline timeout is + * load-dependent, as the frequency of array switched decreases with + * increasing number of running tasks. We also ignore the interactivity + * if a better static_prio task has expired: + */ +#define EXPIRED_STARVING(rq) \ + ((STARVATION_LIMIT && ((rq)->expired_timestamp && \ + (jiffies - (rq)->expired_timestamp >= \ + STARVATION_LIMIT * ((rq)->nr_running) + 1))) || \ + ((rq)->curr->static_prio > (rq)->best_expired_prio)) + +/* * __activate_task - move a task to the runqueue. */ static inline void __activate_task(task_t *p, runqueue_t *rq) { - enqueue_task(p, rq->active); + prio_array_t *array = rq->active; + if (unlikely(EXPIRED_STARVING(rq))) + array = rq->expired; + enqueue_task(p, array); rq->nr_running++; } @@ -2461,22 +2480,6 @@ } /* - * We place interactive tasks back into the active array, if possible. - * - * To guarantee that this does not starve expired tasks we ignore the - * interactivity of a task if the first expired task had to wait more - * than a 'reasonable' amount of time. This deadline timeout is - * load-dependent, as the frequency of array switched decreases with - * increasing number of running tasks. We also ignore the interactivity - * if a better static_prio task has expired: - */ -#define EXPIRED_STARVING(rq) \ - ((STARVATION_LIMIT && ((rq)->expired_timestamp && \ - (jiffies - (rq)->expired_timestamp >= \ - STARVATION_LIMIT * ((rq)->nr_running) + 1))) || \ - ((rq)->curr->static_prio > (rq)->best_expired_prio)) - -/* * Account user cpu time to a process. * @p: the process that the cpu time gets accounted to * @hardirq_offset: the offset to subtract from hardirq_count() - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/