From mboxrd@z Thu Jan 1 00:00:00 1970 From: Odin Ugedal Subject: [PATCH v4] sched/fair: Correctly insert cfs_rq's to list on unthrottle Date: Fri, 4 Jun 2021 12:23:14 +0200 Message-ID: <20210604102314.697749-1-odin@uged.al> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=uged.al; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=3Bs3XH4WZd6E/C1uTgCierdB67bFqe7Y81Sb7TkTn2M=; b=gbFYhwn8pOM/7ph23QfoO3M+4l04YwAWr2awCxogavPFl/D4bhWDJamyo33F0xQSWm xBTJa+57nUaVtoY/P+yk9mIeh9vwa/jzw7/WnoKkkGJCPkehsPBDsrv517LUWVxDvbFl P1Gc0zxDggAg1kbe3iI3a9QV8PxV/AEloCb/s1GD/0rV0JvSCGWfy8yZ6vrCJYI9Kpz5 2XcvxSVnHhT9W1CaLhUh5KuzJRWZn5Ua/2Et2hUoxW0zk6tM1W00KE4i0XK+XS6W/3A1 q5tjFIGbWzEwloT3XMgFvAXj0aRL49NNSWj3B6ADCVjhzQe6DEfCfCwvUI6gIlJkBomc cV5w== List-ID: Content-Type: text/plain; charset="us-ascii" To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Odin Ugedal This fixes an issue where fairness is decreased since cfs_rq's can end up not being decayed properly. For two sibling control groups with the same priority, this can often lead to a load ratio of 99/1 (!!). This happen because when a cfs_rq is throttled, all the descendant cfs_rq's will be removed from the leaf list. When they initial cfs_rq is unthrottled, it will currently only re add descendant cfs_rq's if they have one or more entities enqueued. This is not a perfect heuristic. Instead, we insert all cfs_rq's that contain one or more enqueued entities, or it its load is not completely decayed. Can often lead to situations like this for equally weighted control groups: $ ps u -C stress USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 10009 88.8 0.0 3676 100 pts/1 R+ 11:04 0:13 stress --cpu 1 root 10023 3.0 0.0 3676 104 pts/1 R+ 11:04 0:00 stress --cpu 1 Fixes: 31bc6aeaab1d ("sched/fair: Optimize update_blocked_averages()") Signed-off-by: Odin Ugedal --- Changes since v1: - Replaced cfs_rq field with using tg_load_avg_contrib - Went from 3 to 1 patches; one is merged and one is replaced by a new patchset. Changes since v2: - Use !cfs_rq_is_decayed() instead of tg_load_avg_contrib - Moved cfs_rq_is_decayed to above its new use Changes since v3: - (hopefully) Fix config for !CONFIG_SMP kernel/sched/fair.c | 40 +++++++++++++++++++++------------------- 1 file changed, 21 insertions(+), 19 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 794c2cb945f8..eec32f214ff8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -712,6 +712,25 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se) return calc_delta_fair(sched_slice(cfs_rq, se), se); } +static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) +{ + if (cfs_rq->load.weight) + return false; + +#ifdef CONFIG_SMP + if (cfs_rq->avg.load_sum) + return false; + + if (cfs_rq->avg.util_sum) + return false; + + if (cfs_rq->avg.runnable_sum) + return false; +#endif + + return true; +} + #include "pelt.h" #ifdef CONFIG_SMP @@ -4719,8 +4738,8 @@ static int tg_unthrottle_up(struct task_group *tg, void *data) cfs_rq->throttled_clock_task_time += rq_clock_task(rq) - cfs_rq->throttled_clock_task; - /* Add cfs_rq with already running entity in the list */ - if (cfs_rq->nr_running >= 1) + /* Add cfs_rq with load or one or more already running entities to the list */ + if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running) list_add_leaf_cfs_rq(cfs_rq); } @@ -7895,23 +7914,6 @@ static bool __update_blocked_others(struct rq *rq, bool *done) #ifdef CONFIG_FAIR_GROUP_SCHED -static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) -{ - if (cfs_rq->load.weight) - return false; - - if (cfs_rq->avg.load_sum) - return false; - - if (cfs_rq->avg.util_sum) - return false; - - if (cfs_rq->avg.runnable_sum) - return false; - - return true; -} - static bool __update_blocked_fair(struct rq *rq, bool *done) { struct cfs_rq *cfs_rq, *pos; -- 2.31.1