From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 B23F42F3E for ; Fri, 23 May 2025 09:54:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747994067; cv=none; b=CeI/Ql3V3Oa1fEWbH8eRZNH2aylvfIn+o01EcbUCI7e8yBlaK+Ak+olIwMFlM6oUjT73cgZxruFJrwYsARbT6YpuxAhofo77eu3nmKbnF0+pI//0GS+cjIQC5tpQkguaf+8xTvTv4XO5RW8RlGFQrwT3VBQupoHNLBgQ1RzDkOM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747994067; c=relaxed/simple; bh=E8gNIneXWGPjnI07iEOK/Byl8S2wW9tOYjihShZcXoY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=epFqo0Y5TEg2zjFeaDKrUmEed2HMLyT1qqUD8/DNeklBdDX2I108/pTUUXnjwLsppk6ipS+PlV+p9UAGA3VZWYgSfOS3+6RqBkz3Rlq0p1JNn6HurfLBS9DxVuN98IRQWtdKsNgTfWJwRZ/9pzYRrZfj08Wp33kEHIf73pRV8n8= 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=n4X9rZVe; arc=none smtp.client-ip=95.215.58.186 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="n4X9rZVe" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1747994061; 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=rNzhlrTrgf6zoW1XzrBUaGQMb+etBo16vS9kQPgLQhQ=; b=n4X9rZVee6YQEK15TmlRupOQhGROGs4wShiX52st6RNL3S4rjkXFlnuTSuEdiwG+M/4VlU nm26hkGfFusbHhPrvHx62oSNMVqkUMnlZuLL2nttXng/BVu/JnQSBPIrhhf2toQKFjgY9s d7qG9MgsBmwp+1pqlFysl2KGWTi/SVA= Date: Fri, 23 May 2025 17:53:55 +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> <20250523094106.GA1210419@bytedance> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: <20250523094106.GA1210419@bytedance> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/5/23 17:42, Aaron Lu wrote: > On Fri, May 23, 2025 at 05:13:35PM +0800, Chengming Zhou wrote: >> 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. > > Only work when the task is still handled by fair :) > >> >> 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. >> > > There are corresponding callbacks that handle this, e.g. for task group > change, there is task_change_group_fair() that handles PELT detach; for > affinity change, there is migrate_task_rq_fair() does that and for sched > class change, there is switched_from/to() does that. > > Or do I miss anything? migrate_task_rq_fair() only do it when !task_on_rq_migrating(p), which is wakeup migrate, because we already do detach in dequeue_task_fair() for on_rq task migration... You can see the DO_DETACH flag in update_load_avg() called from dequeue_entity(). 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);