From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (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 55E0D32FA00; Wed, 18 Feb 2026 14:20:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771424422; cv=none; b=QP5+zxExXDWbwhZDgRWvEeDr72/bAn/bq6CFxKxiy0PIIpMx10Wnkq16r/huZ5EQAh6jaH3E5K2rxo7vZ8F0rPLho98Phn7tgblLWrMVvVqaY8agszlz/Vrr69W0Rpr8Qm4QLyMZrqG8ta6AHYuvITOZgnoEBGdZqzWfcLVcO7s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771424422; c=relaxed/simple; bh=wQd1/GlJbhrQGcsmPRyXCDBuRblJ6DrdnJfOyv9ytrQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JKR6TtSG43EcU4ncT33ntDmv31AvS+lQ46JjEI0CvNFHnFHsH6d20rWiRFUVw+zAcVsGX5zj1YYC/jr1xiRozHTZ1AtTJCpQvwmQ1tdFn0ehn3ChIR9RwsvT3CFVSetczzWpP5Tp0NoJSQue5ey8bqHqquuANMQ5vSDjlpd/uE8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=qQQ/Fx15; arc=none smtp.client-ip=148.163.158.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="qQQ/Fx15" Received: from pps.filterd (m0356516.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 61I3gtLJ2301761; Wed, 18 Feb 2026 14:20:18 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:date:from:in-reply-to:message-id :mime-version:references:subject:to; s=pp1; bh=rfaKktZX0rgmOILbT OClBEUylYCktdaj1x7BupczWcU=; b=qQQ/Fx15FTaIONn+pob35V7JREOMk5jGl tpXp0XxIEtAd9tlHOm140kNKLr+ycyOAd8crenUrdJmhyle9briSMLJ5ONet2wWp yJRDsgZUwPG1mgEdb1ANaG0MVmTlcZk8g3nZsmUQbVK8CGTluh99+vR7X3wm554i e6tc0m0m6hYxJLlZxCs2wAN8LfOhsvaQPxgpjY99R9pTQlftOnu1ENh1GHwM9C+v 2A91ISvrZ8EgLa+ZIeJhRcprogFAezW4wtm8m2zSBmMQHl3xjVNIgM63LnWotNNZ vrdZT77eBGct9K7oJiLu9c6yCUS+0SrPb4SdflYqCG4hhlJl4BTkQ== Received: from ppma13.dal12v.mail.ibm.com (dd.9e.1632.ip4.static.sl-reverse.com [50.22.158.221]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4caj648ey3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 18 Feb 2026 14:20:18 +0000 (GMT) Received: from pps.filterd (ppma13.dal12v.mail.ibm.com [127.0.0.1]) by ppma13.dal12v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id 61IDb4PK001432; Wed, 18 Feb 2026 14:20:17 GMT Received: from smtprelay05.fra02v.mail.ibm.com ([9.218.2.225]) by ppma13.dal12v.mail.ibm.com (PPS) with ESMTPS id 4ccb2bg31n-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 18 Feb 2026 14:20:17 +0000 Received: from smtpav05.fra02v.mail.ibm.com (smtpav05.fra02v.mail.ibm.com [10.20.54.104]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 61IEKDck33947970 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 18 Feb 2026 14:20:13 GMT Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C241D20043; Wed, 18 Feb 2026 14:20:13 +0000 (GMT) Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A2B3E2004D; Wed, 18 Feb 2026 14:20:13 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.87.85.9]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 18 Feb 2026 14:20:13 +0000 (GMT) From: Heiko Carstens To: Frederic Weisbecker , Alexander Gordeev , Sven Schnelle , Vasily Gorbik , Christian Borntraeger Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Subject: [PATCH 3/9] s390/idle: Add comment for non obvious code Date: Wed, 18 Feb 2026 15:20:06 +0100 Message-ID: <20260218142012.863464-4-hca@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260218142012.863464-1-hca@linux.ibm.com> References: <20260218142012.863464-1-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: I8tMsWU0hwDELJTIVg53Rhvv6W2HRaeH X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjE4MDEyMCBTYWx0ZWRfX6b+dDX4oZU9Q 2OMopSEulipltFfDLjJ8m/ONR6WiSSKcN0ItQvO0xcy9K4+BCr2XYhnMGiCUNtA59Idit7+LVky 9Y7JYOTRab6saj9Asb+RMty/AzM0XYsdLX6JIVYvcr1LYFJVikzx494sdR5hpEgTyd7ZOnprwwv W83HLejDjZywvkWOt7kkACRnESz4LiGR/AO4iEx8IdWumWOpLjMfOIqSTpfH5/iM1yn82VXsMlb 4OJHSTTxAUPqAqFyhf54tZf/Wt6yAN3uwLphqDBLrMgvLhWCpLqf0qDhWSSJ+YHMiftqwNNgDSh MfrZJgf+1ov9CcHJOnc9AyOjqLhtV9mU6IYVZCloljFPNtU83sdGt4IxNMJbOVhAq2DPv7gvLAt Ymc0acVyWCgyW2ET8VbKTTp9qDNUvrevQ9xpBrgwszjuzycKJIlBHWs8w0IuH6LduNxZMC+iP8v LpqFdt2bxmuuxdjYLtA== X-Proofpoint-GUID: I8tMsWU0hwDELJTIVg53Rhvv6W2HRaeH X-Authority-Analysis: v=2.4 cv=U+mfzOru c=1 sm=1 tr=0 ts=6995caa2 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=OTAgdNo29iS1D3tcfewA:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-18_02,2026-02-18_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 bulkscore=0 impostorscore=0 malwarescore=0 spamscore=0 adultscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602180120 Add a comment to update_timer_idle() which describes why wall time (not steal time) is added to steal_timer. This is not obvious and was reported by Frederic Weisbecker. Reported-by: Frederic Weisbecker Closes: https://lore.kernel.org/all/aXEVM-04lj0lntMr@localhost.localdomain/ Signed-off-by: Heiko Carstens --- arch/s390/kernel/idle.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c index 0f9e53f0a068..4e09f126d4fc 100644 --- a/arch/s390/kernel/idle.c +++ b/arch/s390/kernel/idle.c @@ -34,6 +34,15 @@ void update_timer_idle(void) this_cpu_add(mt_cycles[i], cycles_new[i] - idle->mt_cycles_enter[i]); } + /* + * This is a bit subtle: Forward last_update_clock so it excludes idle + * time. For correct steal time calculation in do_account_vtime() add + * passed wall time before idle_enter to steal_timer: + * During the passed wall time before idle_enter CPU time may have + * been accounted to system, hardirq, softirq, etc. lowcore fields. + * The accounted CPU times will be subtracted again from steal_timer + * when accumulated steal time is calculated in do_account_vtime(). + */ lc->steal_timer += idle->clock_idle_enter - lc->last_update_clock; lc->last_update_clock = lc->int_clock; -- 2.51.0