From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout02.his.huawei.com (canpmsgout02.his.huawei.com [113.46.200.217]) (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 6CB7C2D46C0 for ; Wed, 17 Jun 2026 03:56:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.217 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781668601; cv=none; b=kd7BRPAjAdwvdcHecsYJetMEYTnBjZX3DnoBjo4NBo8obVv9K4k3ThZNNI4U6Ln/00198aOAkmwygoiwyuv4XHysigIIG4JWsXoeIBDzd4G9xUxrubQLMt2YIuNioTwyWcA6SxeHaSoKC2txqWw7CCljayOri6BAU4nkatZQULU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781668601; c=relaxed/simple; bh=iMO5wuwwn/wwMJpoOrJisTvYHvvrXgU1eJ7IUBMvCCQ=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=qN+6ZfXBW/a1tfsC4ff+H9lITMD6KcJk/p20FRK407qyusVUc06/tz6yvnCqW5OWCNa+HyRvm2u2NR+QuFah/9mGVpTDHUOp1KJ0N8O6/1PAWCLNTrodxOPILeEEtVASl33K7Yi2pPikJQtY7ehAexqkb2gOxK4xn0IgNPsh/kI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=wVGIKV8T; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=wVGIKV8T; arc=none smtp.client-ip=113.46.200.217 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="wVGIKV8T"; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="wVGIKV8T" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=ra5V+ZXNFuS9rTwRebaTU7MJLMThOSfVvBQOuemxDC8=; b=wVGIKV8Tt9liaM4aTE6YLzGSsDENm0it7oZzgGFOUyzUVpHr7TQ5CK0x4WKkNm3DKqVCc3XSK y9oXwoYiSrmuQbo9eWn4Y/NbAXPa4Wlhy+KsjXVGgP6dDNwwmwqybRkmjXHH1F17/nWy5A6itCd rJ4zNjtKEWbruGWjLt2o9uE= Received: from canpmsgout01.his.huawei.com (unknown [172.19.92.178]) by canpmsgout02.his.huawei.com (SkyGuard) with ESMTPS id 4gg8vs60vzzcZyX; Wed, 17 Jun 2026 11:48:09 +0800 (CST) dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=ra5V+ZXNFuS9rTwRebaTU7MJLMThOSfVvBQOuemxDC8=; b=wVGIKV8Tt9liaM4aTE6YLzGSsDENm0it7oZzgGFOUyzUVpHr7TQ5CK0x4WKkNm3DKqVCc3XSK y9oXwoYiSrmuQbo9eWn4Y/NbAXPa4Wlhy+KsjXVGgP6dDNwwmwqybRkmjXHH1F17/nWy5A6itCd rJ4zNjtKEWbruGWjLt2o9uE= Received: from mail.maildlp.com (unknown [172.19.162.197]) by canpmsgout01.his.huawei.com (SkyGuard) with ESMTPS id 4gg8vl2Pbbz1T4Fg; Wed, 17 Jun 2026 11:48:03 +0800 (CST) Received: from kwepemr500016.china.huawei.com (unknown [7.202.195.68]) by mail.maildlp.com (Postfix) with ESMTPS id DED6640576; Wed, 17 Jun 2026 11:56:33 +0800 (CST) Received: from huawei.com (10.67.174.242) by kwepemr500016.china.huawei.com (7.202.195.68) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Wed, 17 Jun 2026 11:56:33 +0800 From: Chen Jinghuang To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot CC: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Subject: [QUESTION] sched/fair: EEVDF min_slice stalls in parent cgroup with a continuously running child task Date: Wed, 17 Jun 2026 03:33:25 +0000 Message-ID: <20260617033325.1532258-1-chenjinghuang2@huawei.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: kwepems500001.china.huawei.com (7.221.188.70) To kwepemr500016.china.huawei.com (7.202.195.68) Hi all, I observed an unexpected behavior regarding the EEVDF min_slice update mechanism in a hierarchical cgroup v1 setup. It appears that the parent cgroup's min_slice can become stale when a child cgroup contains a continuously running task (100% load, no sleep). The parent's min_slice fails to update when global or entity slices change, until a dequeue/enqueue event occurs in the child cgroup. Here is the topology of the scenario: Root cfs_rq | cgroup A (se A, contains cpu_sim_A) | cgroup A1 (se A1, contains cpu_sim_A1, 100% CPU load) Steps to reproduce: 1. Create cgroup A, and a sub-cgroup A1 under A. 2. Move a task (cpu_sim_A) into cgroup A, and use the syscall __NR_sched_setattr to explicitly set its slice to 3ms. 3. Set the global base_slice_ns to 3ms: echo 3000000 > /sys/kernel/debug/sched/base_slice_ns 4. Move a 100% load task (cpu_sim_A1, which never voluntary sleeps) into cgroup A1. At this point, both cgroup A's min_slice and cgroup A1's min_slice are observed as 0.1ms (the initialized or previous low value). 5. Change the global base_slice_ns to 2.8ms: echo 2800000 > /sys/kernel/debug/sched/base_slice_ns Observations: - cgroup A1's min_slice correctly updates to 2.8ms. - However, cgroup A's min_slice remains unchanged (stuck at 0.1ms). - Even if we use syscall(__NR_sched_setattr) to explicitly set cpu_sim_A's slice in cgroup A to 2.8ms, cgroup A's min_slice still does not update. - The only way to force cgroup A's min_slice to update to 2.8ms is to trigger a dequeue/enqueue cycle for the task in cgroup A1 (e.g., by renice it) It appears that a parent cgroup's min_slice is only updated when its children are enqueued or dequeued. If a child task runs continuously without sleeping, the parent's min_slice gets stuck and ignores any changes to base_slice_ns or individual entity slices. Is this expected by design in EEVDF, or is there a missing update hook? Any insights would be greatly appreciated. Thanks, Chen Jinghuang