From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C83C0EB64DA for ; Wed, 5 Jul 2023 14:49:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232233AbjGEOtx (ORCPT ); Wed, 5 Jul 2023 10:49:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54660 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232706AbjGEOtt (ORCPT ); Wed, 5 Jul 2023 10:49:49 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C70BD1712 for ; Wed, 5 Jul 2023 07:49:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1688568546; 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=UyM5IDrf51eZ/kcZjAxbwOacXO+LNKpyPjbVqqLXG8s=; b=Tcoc7i4oRiAs2zgWcJekxzgSldm4tRAsbFu8dl2oOsAeHrkfbLRLvEy/OJxi6qh3IJJar7 PxGROIqyXvguySgwFAUkWYd8sljXTHAMP5uy22OePubpdU2DQMDJiLzsGEYUtmXUu8F/NI PbF3BFR7b6xiXDRcALAX84kVsA5V/5E= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-434-pI7A_wqlP9eWF9sY32YdEA-1; Wed, 05 Jul 2023 10:49:03 -0400 X-MC-Unique: pI7A_wqlP9eWF9sY32YdEA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D0CD8185A7A2; Wed, 5 Jul 2023 14:49:02 +0000 (UTC) Received: from [10.22.8.133] (unknown [10.22.8.133]) by smtp.corp.redhat.com (Postfix) with ESMTP id 67DBF2166B25; Wed, 5 Jul 2023 14:49:02 +0000 (UTC) Message-ID: Date: Wed, 5 Jul 2023 10:49:02 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask() Content-Language: en-US To: Miaohe Lin Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, tj@kernel.org, hannes@cmpxchg.org, lizefan.x@bytedance.com References: <20230704113049.1019118-1-linmiaohe@huawei.com> <33c2bf85-6def-fce9-9ea7-3b3e80db67b7@huawei.com> From: Waiman Long In-Reply-To: <33c2bf85-6def-fce9-9ea7-3b3e80db67b7@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/5/23 01:56, Miaohe Lin wrote: > On 2023/7/5 11:14, Waiman Long wrote: >> On 7/4/23 07:30, Miaohe Lin wrote: >>> kthread_is_per_cpu() can be called directly without checking whether >>> PF_KTHREAD is set in task->flags. So remove PF_KTHREAD check to make >>> code more concise. >>> >>> Signed-off-by: Miaohe Lin >>> --- >>>   kernel/cgroup/cpuset.c | 2 +- >>>   1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >>> index 58e6f18f01c1..601c40da8e03 100644 >>> --- a/kernel/cgroup/cpuset.c >>> +++ b/kernel/cgroup/cpuset.c >>> @@ -1230,7 +1230,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus) >>>               /* >>>                * Percpu kthreads in top_cpuset are ignored >>>                */ >>> -            if ((task->flags & PF_KTHREAD) && kthread_is_per_cpu(task)) >>> +            if (kthread_is_per_cpu(task)) >>>                   continue; >>>               cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus); >>>           } else { >> The initial intention was to ignore only percpu kthreads. The current code likely ignore all the kthreads. Removing the PF_KTHREAD flag, however, may introduce unexpected regression at this point. I would like to hold off for now until more investigation are done. > IMHO, the current code will ignore only percpu kthreads: > 1.If PF_KTHREAD is set in task->flags, this patch doesn't make any difference. > 2.If PF_KTHREAD is not set in task->flags, kthread_is_per_cpu will *always return false*. So this patch doesn't make any functional change. > > bool kthread_is_per_cpu(struct task_struct *p) > { > struct kthread *kthread = __to_kthread(p); > if (!kthread) > return false; > .... > } > > static inline struct kthread *__to_kthread(struct task_struct *p) > { > void *kthread = p->worker_private; > if (kthread && !(p->flags & PF_KTHREAD)) > ^^^^^^^^^^^^^^^^^^^^^^ > PF_KTHREAD is not set, so kthread = NULL. > kthread = NULL; > return kthread; > } > > Or am I miss something? Thanks for comment and review. Yes, you are right. I was that conscious when I reviewed the patch last night :-) Reviewed-by: Waiman Long