From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=90.155.92.199 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794052980; b=vgkA9UPQeKvwpMJAZLfiOijYLqJhUuyYc5accLTS8mSEeZnRbd8guVwIU1PzsVD1zGuz qlrDqmJp1uj/TVBBVNBofAS5Q1ntCg05NOiZ57SRjKcclEtQoveRcDryfhpvtaUfX79wa fL/0Y2JluT1NrW7yU4nLlg4kOmz64eZOVDSy5V1nZNhks8Mo91Jh4/crkrN+0fDWpJzBg 5JItfz+/rVVf+JnEsgaegt8bHu2ii+Mgjio4UdWweFDmgKGdhhTf7IaWiy7vG33OvrkzO uwfLlLQTsDt+rojsCVXZ9+iP2gtq9di9j0n7N1/ptHg93wcW+6U/ILsdcwHQChki8EA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794052980; h=DMARC-Filter:DKIM-Signature:Received:Received:Message-ID:User-Agent: Date:From:To:Cc:Subject:References:MIME-Version:Content-Type; bh=dzmn5OvuL6HWddApDFOpicmssA7vwWfg++lvft7UzdE=; b=tYhmC3TX2eW1rLS2bZ5R7dXe1FfhSB4q2ze64Pj+11S2oH9lW2+rDtrUBuojmR7JBH5D kYwpFWx+x9KNIu6/GFumxOx0SQ9Y144x6dirJd65/x5DPaLe9/zZdpSo7wZDeogm8m2xR W44+lBMaG7Bu+s7ajsuXqiCGIVuO0vTaqxAreQBiI8sLxrsrClUWC/pqWE0xIl/eFsbaS x5l2O2WPiKTMei7A6cFobznHpRnmqn44rGI8yo+yjPbIi7oN9tMtSALor22zRhQsgIqT8 jT+i9oeEIIwwnCx6mFXNcuCXEP6IYd64a9BLLEDPfXd20YDbV7gaFvvrD9D+AHBlIhQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=i0HWzt7v; arc=none smtp.remote-ip=90.155.92.199 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7BEA5606A338 for ; Sat, 7 Nov 2026 12:02:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 7BEA5606A338 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.a=rsa-sha256 header.s=desiato.20200630 header.b=i0HWzt7v DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=dzmn5OvuL6HWddApDFOpicmssA7vwWfg++lvft7UzdE=; b=i0HWzt7vUpyKm9YiG6cRoROZCV I/cT62+40Jv/VOLZ3cvVrcH5TxIHbhGQAqJOALyFdDDvXKf5LhKjU2hB7yDXmzcCOt1rFMvyTVEB1 gOPUP7lxmXblwiuwMdxl7hV5L3lJ9BFZB8KKBD9AfkNiWSA8x6cfXk4GRaolLF5oxNyySplquvPgJ jz01VjAu92KIUjQcuyEukOlH9NzQuW6B8ubia8PhX0h0OxC/hnSJITVS6IC0J4EagcYGZSUnPtfws 70FZrPkEqHmqR1dOsfiWxJcuMw4wLr0r6/mGyXTd9YW/nSzC4C14IU/BgeWaNIQYZiAnYZYWYq0Vm pX23FfGQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.100.1 #2 (Red Hat Linux)) id 1xPf8B-00000005BYi-1t1g; Sat, 07 Nov 2026 12:02:47 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 319F730312D; Sat, 07 Nov 2026 13:02:45 +0100 (CET) Message-ID: <20261107120207.655754098@infradead.org> User-Agent: quilt/0.68 Date: Sat, 07 Nov 2026 12:59:21 +0100 From: Peter Zijlstra To: mingo@kernel.org Cc: 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, linux-kernel@vger.kernel.org, tj@kernel.org, ziqianlu@bytedance.com Subject: [PATCH v2 08/12] sched/core: Allow newidle for core-sched References: <20261107115913.261163891@infradead.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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. Avoids the 'stealing', but doesn't yet enable newidle just yet. [1] https://patch.msgid.link/20260603095108.GA1684319@bytedance.com Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/core.c | 3 ++- kernel/sched/fair.c | 3 ++- kernel/sched/sched.h | 15 ++++++++++++++- 3 files changed, 18 insertions(+), 3 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3065,7 +3065,8 @@ static int affine_move_task(struct rq *r return -EINVAL; } - if (task_on_cpu(rq, p) || READ_ONCE(p->__state) == TASK_WAKING) { + if (task_on_cpu(rq, p) || task_on_core(rq, p) || + READ_ONCE(p->__state) == TASK_WAKING) { /* * MIGRATE_ENABLE gets here because 'p == current', but for * anything else we cannot do is_migration_disabled(), punt --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11184,7 +11184,8 @@ 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 @@ -1594,6 +1594,14 @@ 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) @@ -1639,6 +1647,11 @@ 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 @@ -4269,7 +4282,7 @@ 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;