From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 EE8431F94F for ; Wed, 24 Jun 2026 12:27:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782304026; cv=none; b=aRpr/l+rlE/e5Z3TSsoAZblXHTWqriUZ8O2n8u3A656r1dDln+wFAblTlVZG+ZYhNfxO0EVDDtqmoUDKUeYNrTUmWewr5O0Aw1o67J7r+0QsVTAsRObvVObRywCstEasDqvxESBJg8sPyYuvXR2y6qmmVGuSWuEaVpE4qrcOKHE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782304026; c=relaxed/simple; bh=9GQMNm2TNt65KXAxml+iUTngcTbytepIX7TEsbRYWww=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=gEyDOTQxhPOvFy4cRee5xPldau9+xs+HUSATbOeVGG4StNpMeg+MCLsjCXCM3eCZyLw46aPXRKBroJiNmTcIokjQAl4niQ0LkmBeXvS/z9GUtkMWJqWmiV5KLdcgA1a/amT3v3ZhBg9/COb0DQUazGj6eYvbYCFul4SpmSO7r5Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=abZI1UMP; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="abZI1UMP" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=wdqXaK5c5qprsVuRiIwLRfWDd98zSavtLVF75raKAsU=; b=abZI1UMPrUevELwJ/FJhLnPs29 hoZdHW7yfvmrCqPUPW7MtYlFb90YUkiY6z/d9pzOKnjVC3bsFUo3nXeatyCuqTFqc6iqEzxedyEM1 oAgUOfvr4TSjN/guCvsksgOKuU9MSXDlR1QnK3MArswxV4naZq9Nghr7tfaHHIlwmxmB4ay20hcVq GvJZebTGncdQUAsdOoesOW680aLuTnTWGHjaHZGqZmKuZ8QwDflZMrrJGwYwoJ4DSH7zmn22WKrgh rnhjFmUm7gEyqPgH4wuq2UygeMaS5KlyD8KkNujnnuVZd/pMsEbvTWYaAOwDNmwPxA13kIMCPFOzc QiIui3Ig==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wcMgt-000000080iZ-2SjI; Wed, 24 Jun 2026 12:26:52 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id EC088300BDE; Wed, 24 Jun 2026 14:26:50 +0200 (CEST) Message-ID: <20260624122451.583174198@infradead.org> User-Agent: quilt/0.68 Date: Wed, 24 Jun 2026 14:13:28 +0200 From: Peter Zijlstra To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, ziqianlu@bytedance.com, tj@kernel.org, williams@redhat.com, jkacur@redhat.com Subject: [PATCH 1/2] sched/core: Allow newidle for core-sched References: <20260624121327.190063948@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 As reported [1], it is possible for newidle, as called from pick_task_fair(), to migrate a task that was already selected for the SMT sibling. That is, in case of core scheduling (pick_next_task()'s restart_multi label), pick_task() is called for each SMT sibling. Suppose SMT0 picks task A, and SMT1 has no tasks and does newidle, it must not be possible (but currently is) to migrate A to SMT1 and also select A. This re-enables newidle balancing for core scheduling. [1] https://patch.msgid.link/20260603095108.GA1684319@bytedance.com Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/fair.c | 6 ++---- kernel/sched/sched.h | 15 ++++++++++++++- 2 files changed, 16 insertions(+), 5 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9942,9 +9942,6 @@ struct task_struct *pick_task_fair(struc return p; idle: - if (sched_core_enabled(rq)) - return NULL; - new_tasks = sched_balance_newidle(rq, rf); if (new_tasks < 0) return RETRY_TASK; @@ -10783,7 +10780,8 @@ int can_migrate_task(struct task_struct env->flags &= ~LBF_ALL_PINNED; if (task_on_cpu(env->src_rq, p) || - task_current_donor(env->src_rq, p)) { + task_current_donor(env->src_rq, p) || + task_on_core(env->src_rq, p)) { schedstat_inc(p->stats.nr_failed_migrations_running); return 0; } --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1570,6 +1570,14 @@ static inline bool task_has_sched_core(s return !!p->core_cookie; } +static inline bool task_on_core(struct rq *rq, struct task_struct *p) +{ + if (sched_core_disabled()) + return false; + + return rq->core_pick == p; +} + #else /* !CONFIG_SCHED_CORE: */ static inline bool sched_core_enabled(struct rq *rq) @@ -1615,6 +1623,11 @@ static inline bool task_has_sched_core(s return false; } +static inline bool task_on_core(struct rq *rq, struct task_struct *p) +{ + return false; +} + #endif /* !CONFIG_SCHED_CORE */ #ifdef CONFIG_RT_GROUP_SCHED @@ -4131,7 +4144,7 @@ void move_queued_task_locked(struct rq * static inline bool task_is_pushable(struct rq *rq, struct task_struct *p, int cpu) { - if (!task_on_cpu(rq, p) && + if (!task_on_cpu(rq, p) && !task_on_core(rq, p) && cpumask_test_cpu(cpu, &p->cpus_mask)) return true;