From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 4298226F2B6 for ; Thu, 18 Dec 2025 07:14:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766042061; cv=none; b=SzIWQlCn2O3Qf7mtygDLyPFct1oj5X8t2JR5Q3qBiJy8sIVKjRfaxzzAGEi4nCgix3iCRCUKGw4Aw1ql1T9ZwXrATaGuNoADIfUJ+3VesQ/9/YaJLCt0xvPT0v7DB8uvveUsUdz/WamRLfjeEjnZtfaWUdqsXOnzNnlMHhnYS5Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766042061; c=relaxed/simple; bh=pdMUtduMXCj5whENGA9N7DnLbY+JEMVMPlaas2KdqgI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Zgfj1n5gb/FvIt1cByRPBTvcxjS6/QEXTCzen5eyWYqsiUjcY2peiKfHN0S5MHe4A9FuBqxsFmvNgiWY368SiILCfwpcWsiZLLB9wKcx8QHhzfkf+l7x9kWB0M+sg2mRYNDM4e31qnd4MnbRVg2k3G9IPXGquZs0stkepW3NzW4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=UtWQgTcB; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=kD6QzC6G; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UtWQgTcB"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="kD6QzC6G" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1766042059; 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: in-reply-to:in-reply-to:references:references; bh=oNBsiLM1lI5WSv0gDo/xxnKGXTG+8RkXyoth8Hg52dk=; b=UtWQgTcBr3AZWEy1jhWAP0bDuaGCQJTMMT+/p6cmNv+M1uKaMgTdBPkIyWMqpCA5mM18As v/9Ym2hI8MvDZQXWBHIaiNrP18TtjDwSkCXXG+HoEcaw8F34EWgBWSpAaPprX9rcSvKg2q 7V0BPshHNlmEzjZxVNeK9Mx1Ee7g9PI= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-489-K8ab3iJVO-GawLKxEiB9Cw-1; Thu, 18 Dec 2025 02:14:17 -0500 X-MC-Unique: K8ab3iJVO-GawLKxEiB9Cw-1 X-Mimecast-MFC-AGG-ID: K8ab3iJVO-GawLKxEiB9Cw_1766042056 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-430f5dcd4d3so155124f8f.1 for ; Wed, 17 Dec 2025 23:14:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1766042056; x=1766646856; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=oNBsiLM1lI5WSv0gDo/xxnKGXTG+8RkXyoth8Hg52dk=; b=kD6QzC6GiQmYrdH4YxH7W2Gj77eHBrbcWvGvJrulBJpYs+ya+7f8fIv2uGgQ/O0B8m Fz5DMDxstvMDHrBdM9GMU7QwEwy3bf5WMX+/P6PwdEyqeYwxl/GWkR07iF9RrfU0o7lB 3MPWhG8+PXQ7wScmUJ4OdtSas1SCuLGgmlcBJmnZnOVGOFO61pjbyxw0EKpdH8OQPT0E cR+jwyalByW5W7wGf55tLF07tR3HUrgxRmANRCgN9sr/UxY3IqtHidQgJLpgKs59WYJF b7aDvWN3u+6BOPkN/pKUbKUzmhkFmb2XRgZNpQFjxFFt27qUHL2OByawW7JVhtbUUAG+ l33g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1766042056; x=1766646856; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=oNBsiLM1lI5WSv0gDo/xxnKGXTG+8RkXyoth8Hg52dk=; b=gd+sVBWKNw0UoqzGBsYgmE2jcV4eYf6lbPE4SNoPCEQQ8BNQGaRKFDrzKORiCEfE5u KDOgXfMZQfuWBkqHnB7fmBL7viCeFyNfOZSosdCmnHHt2eujn+KtsHxFi88ONWunn2T7 sfZOKjUWV+f303GNTIbKc/SWM0d3hRBdyPh3uWBVt2z3uvCjjlNwF3Yz9f+B09ljfopX AgUKCDTu0KrgIXOkfa/6ANF4xu5KUQS9yK96WQ+OBB7eZm2dFIoYyxMAOw/0IF8BEdkb Mlo02Rb+BEyYYowwCYpWMNTVYJ6bXDRY1Ux1QOXlNtcUEqHg4NuQpoo1T8CKNFD5yLn4 KsQA== X-Forwarded-Encrypted: i=1; AJvYcCVRKD+CMiMNY7aBphRcPFbfzupfxYlrAjdM7DUDnuyqyXrm1KpoQa2yynlniubsBBzNvmRWX5cKy2axWmo=@vger.kernel.org X-Gm-Message-State: AOJu0YzG2QEEbLuIaG0GQ3PsGprQ+lExZAHZcU7X6tKHc6FeWlMyexfW 9xYvdzPX+zOoN2MmK+JPIoo+RdEsHcY7KLPKZorJHrrwq/o2wHVJRLYNqJx+mWJVjgpBR4F28Xx tkaTC9+vt9Z+N5jY2U1O5c9NtdgC734aiC33A6K0ClS6yN9aBsUTmDNYGHS7KnD4s7g== X-Gm-Gg: AY/fxX6LSth+mIDAIdVvaXYooFQ+DipThlv/xqSK79zLQekME/bC1Y8MdXdV/X7t9Sv YpfXkQvpUUHwwRlwPCXkshL8DHNEIvH/Ogq+/xcAzY0fToAR1QCbctsWPrl5fBbvrdMWwMkry4M nBSFQShtjEHj/j1GnHExL5ysJ42sHewPARVCH5KH+0oBX85mw950fwkUGMyeWm7wucQpEaLcnzL 5L+W4alOXQf3OA4tv29BGaFDQvy8dZ5KBQgAoXeLtKLA2mdFr1C9a91es+SLJP9Nj8e4oztF0bK p9YKy+6SBSvmXDYnc7/AYwyxyPEHW9RweDowEgCj17EmTnd0WsUZZRUBc8brRaT/T+qCg6b2Q2x EaJTy5+/QyLE1cfcAuAMbneh9A5gtxbBt6b7J1GGq X-Received: by 2002:a05:6000:3113:b0:430:fbce:458a with SMTP id ffacd0b85a97d-432448b7f11mr2026713f8f.18.1766042056123; Wed, 17 Dec 2025 23:14:16 -0800 (PST) X-Google-Smtp-Source: AGHT+IHmwvfPARt5/oktdF01vTTh+pbj0DvIQNLkJ0QsqlEvJKz7q81ZhZQ2a/z1plKZxslmFO/O2g== X-Received: by 2002:a05:6000:3113:b0:430:fbce:458a with SMTP id ffacd0b85a97d-432448b7f11mr2026688f8f.18.1766042055684; Wed, 17 Dec 2025 23:14:15 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.129.40]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324493fe27sm3248198f8f.12.2025.12.17.23.14.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Dec 2025 23:14:15 -0800 (PST) Date: Thu, 18 Dec 2025 08:14:13 +0100 From: Juri Lelli To: Andrea Righi Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Tejun Heo , David Vernet , Changwoo Min , Shuah Khan , Joel Fernandes , Christian Loehle , Emil Tsalapatis , sched-ext@lists.linux.dev, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/7] sched_ext: Add a DL server for sched_ext tasks Message-ID: References: <20251217093923.1556187-1-arighi@nvidia.com> <20251217093923.1556187-5-arighi@nvidia.com> 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=us-ascii Content-Disposition: inline In-Reply-To: Hi! On 17/12/25 22:55, Andrea Righi wrote: > sched_ext currently suffers starvation due to RT. The same workload when > converted to EXT can get zero runtime if RT is 100% running, causing EXT > processes to stall. Fix it by adding a DL server for EXT. > > A kselftest is also included later to confirm that both DL servers are > functioning correctly: > > # ./runner -t rt_stall > ===== START ===== > TEST: rt_stall > DESCRIPTION: Verify that RT tasks cannot stall SCHED_EXT tasks > OUTPUT: > TAP version 13 > 1..1 > # Runtime of FAIR task (PID 1511) is 0.250000 seconds > # Runtime of RT task (PID 1512) is 4.750000 seconds > # FAIR task got 5.00% of total runtime > ok 1 PASS: FAIR task got more than 4.00% of runtime > TAP version 13 > 1..1 > # Runtime of EXT task (PID 1514) is 0.250000 seconds > # Runtime of RT task (PID 1515) is 4.750000 seconds > # EXT task got 5.00% of total runtime > ok 2 PASS: EXT task got more than 4.00% of runtime > TAP version 13 > 1..1 > # Runtime of FAIR task (PID 1517) is 0.250000 seconds > # Runtime of RT task (PID 1518) is 4.750000 seconds > # FAIR task got 5.00% of total runtime > ok 3 PASS: FAIR task got more than 4.00% of runtime > TAP version 13 > 1..1 > # Runtime of EXT task (PID 1521) is 0.250000 seconds > # Runtime of RT task (PID 1522) is 4.750000 seconds > # EXT task got 5.00% of total runtime > ok 4 PASS: EXT task got more than 4.00% of runtime > ok 1 rt_stall # > ===== END ===== > > v5: - do not restart the EXT server on switch_class() (Juri Lelli) > v4: - initialize EXT server bandwidth reservation at init time and > always keep it active (Andrea Righi) > - check for rq->nr_running == 1 to determine when to account idle > time (Juri Lelli) > v3: - clarify that fair is not the only dl_server (Juri Lelli) > - remove explicit stop to reduce timer reprogramming overhead > (Juri Lelli) > - do not restart pick_task() when it's invoked by the dl_server > (Tejun Heo) > - depend on CONFIG_SCHED_CLASS_EXT (Andrea Righi) > v2: - drop ->balance() now that pick_task() has an rf argument > (Andrea Righi) > > Tested-by: Christian Loehle > Co-developed-by: Joel Fernandes > Signed-off-by: Joel Fernandes > Signed-off-by: Andrea Righi > --- This new version looks good to me, thanks! Reviewed-by: Juri Lelli Best, Juri