From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 574C52652AF; Wed, 24 Jun 2026 23:55:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782345334; cv=none; b=M55rw4GHHFPPx9r4Jil5nBR+oOt9QsNQAD+6v8+uSkBL6WRmTCONfnwNNHqvP98Kvag7rl5dFdWKHvyU7hgS4/GGIwSWEoY/+ewv88K4xwR14Jdns4yvGShTatbSRw97y6KXB2W5f8IXgofNrdUP6zat+SKJhSJsdpROLm/Q/YU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782345334; c=relaxed/simple; bh=DWEPJCpu3QrDhwamWRIGJd5NNzLE4XGS1Kb9dC3L84k=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=oFj6VF5I/sLs7acyyEw7CoaAOrFKXeChnBypgKgDKW7emzM46YCJif5yLRPYfwZtI5ZlL10cMXVaqUVT66Npzfn9zW+p2KUieM3E7B9gdOUoapVebPmYjdEzISR3IVc6daxZ4sO3KX+A8ZUqHlamQs/LB/kLJNNmwdvx4hx3Gbw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dzcGdO+M; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dzcGdO+M" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BF7B01F000E9; Wed, 24 Jun 2026 23:55:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782345333; bh=dlZuFnUplu825VpNYh4LDqSTV0APJIi+I856VEvhJiM=; h=From:To:Cc:Subject:Date; b=dzcGdO+M/Bfk5wFr4YMsszGvLXsb3fev580xNZEkMv2tUX6Uf5pdn7uxKdlKlSadq Zy+S/Bnpa5ksLf3YUfGrEIlHDciOh0wO2mNEpoH4vBvAwxDwhaHBhPvN7you9MDxbG 9CHHHtTTCxfknf7KbmkoY/s1VlIU6t5CHBydXuY9L3Gk93q0+GZAkcGyhd5X65SfgJ bz11dQXsw10bpSx9XK9QzxY7P9K94O7vDeUaJW1tCNQT9AEq9TFCpk+aPk8VGHl7+G 0r1aNzqkr+ZjJZy4010cn2etIawRceH2kKPvFn3AjfTdbe9Iv1wCqDs600+OV3IRnk uSbb+7IPY5xdg== From: Tejun Heo To: David Vernet , Andrea Righi , Changwoo Min , sched-ext@lists.linux.dev Cc: Emil Tsalapatis , linux-kernel@vger.kernel.org Subject: [PATCH] sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx() Date: Wed, 24 Jun 2026 13:55:31 -1000 Message-ID: <20260624235531.2979880-1-tj@kernel.org> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit put_prev_task_scx() warns when a runnable task drops to a lower sched_class without SCX_OPS_ENQ_LAST, assuming balance_one() would otherwise keep it running. Under core scheduling that assumption is wrong: a forced-idle SMT sibling reschedules through the core_pick fast path in pick_next_task(), which skips balance() for the CPU, so balance_one() never runs and a runnable task can drop to idle with ENQ_LAST unset. Skip the warning when core scheduling is enabled. Fixes: 7c65ae81ea86 ("sched_ext: Don't call put_prev_task_scx() before picking the next task") Signed-off-by: Tejun Heo --- kernel/sched/ext/ext.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c index 9c9cb9d08bca..503c4d2105ee 100644 --- a/kernel/sched/ext/ext.c +++ b/kernel/sched/ext/ext.c @@ -3092,7 +3092,9 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p, * which should trigger an explicit follow-up scheduling event. */ if (next && sched_class_above(&ext_sched_class, next->sched_class)) { - WARN_ON_ONCE(!(sch->ops.flags & SCX_OPS_ENQ_LAST)); + /* core-sched can force cpu idle while @p is runnable */ + if (!sched_core_enabled(rq)) + WARN_ON_ONCE(!(sch->ops.flags & SCX_OPS_ENQ_LAST)); do_enqueue_task(rq, p, SCX_ENQ_LAST, -1); } else { do_enqueue_task(rq, p, 0, -1);