From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta0.migadu.com (out-182.mta0.migadu.com [91.218.175.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E634A7083A for ; Fri, 23 May 2025 09:13:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747991632; cv=none; b=lV+EXCBBQyJfldUSMKXP4xXxoJdnXKIOs8+l5L5tLxiQog+1USFZ2pynDP/n3lp5i3EfwWizcKObDF2mE4MbLaIokgRYfRaoUwBUX7k0NF3fAiWmLZPrKOllkLezBwufoy3pBf9YYMf1wJo0/gSeMJhlFWZTjSOdS/yA641mhz0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747991632; c=relaxed/simple; bh=pp+5mDH2gMMXhtXtH9FdhI4aZtydoi5eV/fiWABgzH0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GSRyNUbnv3w4nlpgUqnPTlpDsUIAuwBvDnYQmpChaAbwhVmiNzYfA3+hdo4Po+/p30t4QHpoYtXNcwUK4g1dSFqpi5dl11MJaWfZ9vlBqPNn0IZLAhTO2E3oaRErpho2bmhpHmjDmFqNN2FbvrFbBXkc42mPsiciyhh/AmCCQGw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=OCNVAyAl; arc=none smtp.client-ip=91.218.175.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="OCNVAyAl" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1747991626; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dp722LMb6J2j+bcRYsjmWZrd3CzRH5/sf16/l7rDboc=; b=OCNVAyAlMxCuI23Fva2H9a0TJxEPuwCc9PcM8gFBO+yKQgnO/BOvToWb9+NOFYaJdLIP5s J2epBFOOXSyrZUbKv2NtVdcKOuuJIlXKOdsYna+zKV8+1KRHFyX4DvIVXNj0gxnoPgaahp kYtn7mEGf0+oRPQCwVWYDyiqDVbXqNk= Date: Fri, 23 May 2025 17:13:35 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 4/7] sched/fair: Take care of group/affinity/sched_class change for throttled task To: Aaron Lu Cc: Valentin Schneider , Ben Segall , K Prateek Nayak , Peter Zijlstra , Josh Don , Ingo Molnar , Vincent Guittot , Xi Wang , linux-kernel@vger.kernel.org, Juri Lelli , Dietmar Eggemann , Steven Rostedt , Mel Gorman , Chuyi Zhou , Jan Kiszka , Florian Bezdeka References: <20250520104110.3673059-1-ziqianlu@bytedance.com> <20250520104110.3673059-5-ziqianlu@bytedance.com> <63237b23-ae10-45f9-abdd-8ea4adb4d15e@linux.dev> <20250523075640.GA1168183@bytedance> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: <20250523075640.GA1168183@bytedance> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/5/23 15:56, Aaron Lu wrote: > On Fri, May 23, 2025 at 10:43:53AM +0800, Chengming Zhou wrote: >> On 2025/5/20 18:41, Aaron Lu wrote: >>> On task group change, for tasks whose on_rq equals to TASK_ON_RQ_QUEUED, >>> core will dequeue it and then requeued it. >>> >>> The throttled task is still considered as queued by core because p->on_rq >>> is still set so core will dequeue it, but since the task is already >>> dequeued on throttle in fair, handle this case properly. >>> >>> Affinity and sched class change is similar. >> >> How about setting p->on_rq to 0 when throttled? which is the fact that >> the task is not on cfs queue anymore, does this method cause any problem? >> > > On task group change/affinity change etc. if the throttled task is > regarded as !on_rq, then it will miss the chance to be enqueued to the > new(and correct) cfs_rqs, instead, it will be enqueued back to its > original cfs_rq on unthrottle which breaks affinity or task group Yeah, this is indeed a problem, I was thinking to delete the throttled task from the cfs_rq limbo list, then add it to another cfs_rq limbo list or cfs_rq runnable tree based on the new cfs_rq's throttle status. But it's much complex compared with your current method. > settings. We may be able to do something in tg_unthrottle_up() to take > special care of these situations, but it seems a lot of headaches. > > Also, for task group change, if the new task group does not have throttle > setting, that throttled task should be allowed to run immediately instead > of waiting for its old cfs_rq's unthrottle event. Similar is true when > this throttled task changed its sched class, like from fair to rt. > > Makes sense? Ok, the another problem of the current method I can think of is the PELT maintenance, we skip the actual dequeue_task_fair() process, which includes PELT detach, we just delete it from the cfs_rq limbo list, so it can result in PELT maintenance error. Thanks! > > Thanks, > Aaron > >>> >>> Signed-off-by: Aaron Lu >>> --- >>> kernel/sched/fair.c | 24 ++++++++++++++++++++++++ >>> 1 file changed, 24 insertions(+) >>> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>> index 74bc320cbc238..4c66fd8d24389 100644 >>> --- a/kernel/sched/fair.c >>> +++ b/kernel/sched/fair.c >>> @@ -5866,6 +5866,10 @@ static void throttle_cfs_rq_work(struct callback_head *work) >>> update_rq_clock(rq); >>> WARN_ON_ONCE(!list_empty(&p->throttle_node)); >>> dequeue_task_fair(rq, p, DEQUEUE_SLEEP | DEQUEUE_SPECIAL); >>> + /* >>> + * Must not add it to limbo list before dequeue or dequeue will >>> + * mistakenly regard this task as an already throttled one. >>> + */ >>> list_add(&p->throttle_node, &cfs_rq->throttled_limbo_list); >>> resched_curr(rq); >>> } >>> @@ -5881,6 +5885,20 @@ void init_cfs_throttle_work(struct task_struct *p) >>> INIT_LIST_HEAD(&p->throttle_node); >>> } >>> +static void dequeue_throttled_task(struct task_struct *p, int flags) >>> +{ >>> + /* >>> + * Task is throttled and someone wants to dequeue it again: >>> + * it must be sched/core when core needs to do things like >>> + * task affinity change, task group change, task sched class >>> + * change etc. >>> + */ >>> + WARN_ON_ONCE(p->se.on_rq); >>> + WARN_ON_ONCE(flags & DEQUEUE_SLEEP); >>> + >>> + list_del_init(&p->throttle_node); >>> +} >>> + >>> static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags); >>> static int tg_unthrottle_up(struct task_group *tg, void *data) >>> { >>> @@ -6834,6 +6852,7 @@ static inline void sync_throttle(struct task_group *tg, int cpu) {} >>> static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {} >>> static void task_throttle_setup_work(struct task_struct *p) {} >>> static bool task_is_throttled(struct task_struct *p) { return false; } >>> +static void dequeue_throttled_task(struct task_struct *p, int flags) {} >>> static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq) >>> { >>> @@ -7281,6 +7300,11 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags) >>> */ >>> static bool dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) >>> { >>> + if (unlikely(task_is_throttled(p))) { >>> + dequeue_throttled_task(p, flags); >>> + return true; >>> + } >>> + >>> if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags & DEQUEUE_SAVE)))) >>> util_est_dequeue(&rq->cfs, p);