From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (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 2A8353A1E9F for ; Tue, 6 Jan 2026 06:44:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.156.1 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767681885; cv=none; b=ixkbK0cDofkqevV/TzXxUVQz2TbNn5OxStjFsTLTuas6nkNBL7V3VlqEpeGxoFgHm/meGYhE6Y5bcv/NKGH6hwL1CmSBebhqMs9iU3NKiCMFFnPXWUc3LQ+0MjpTw7N0HnI0lteFEbrJclDo3bYorVP2X5QlTRBwM85ODaWzo5s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767681885; c=relaxed/simple; bh=Zg2J+YAHRPHxd3/KAkLLiocZD/r+XPVmuGlQlbdwHDM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eDCakDZKjseymRrS2jPdSo8B4l4Afd/ZSsvdQxbFPlSwKDAsFuqstbKeC3WeES7HeIqHCbXuJK5Gt4U99pyT3VPe+3X2H3vYbXe1aaIz2IrLkCZaDBxatVJRBO9E9JLOfkwFvUfqBAd21PBlw2B87KU2YBCY3Vb2mJMcGzCYiFs= 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=RDow5jna; arc=none smtp.client-ip=148.163.156.1 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="RDow5jna" Received: from pps.filterd (m0360083.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 6066GCXs026728; Tue, 6 Jan 2026 06:44:12 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=edfZ15 k1C43QhlsIo6Qis01ew7FdLQSI1vw6T34YSq8=; b=RDow5jna6bwxIobHe2v70S 35sceyVpiPLcrNL5upl4dX3TsjIZkg/6EDG7R1DVaI6vILX03kWpCoVA53QCF7mb HLtE1EcvcZB69WHZpNRa98pSiT6247MZeFeaEkGshJTd2xnqzYKPaP5Wm6P9/XLf CmhueuSAY1cBpmkaNJJwFsncOJ28JJD91w0QfwFBLGyN3Mh+mpg9LxqRU9WU5LJE kOhlyQvJk8l5sO1D2CyQ1dAQ/UV2aSMXZhYl50cnLfUEv+tEG7BiYkSCDjJvuqsD EY87H7Rla4QtH6VJO7hUWkrAAaEyjn75JmiTuO3OO0KDWWaUAQdhKH6k+dSAqmLQ == Received: from ppma21.wdc07v.mail.ibm.com (5b.69.3da9.ip4.static.sl-reverse.com [169.61.105.91]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4betm72q9x-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 06 Jan 2026 06:44:12 +0000 (GMT) Received: from pps.filterd (ppma21.wdc07v.mail.ibm.com [127.0.0.1]) by ppma21.wdc07v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id 606529Xx014511; Tue, 6 Jan 2026 06:44:11 GMT Received: from smtprelay07.fra02v.mail.ibm.com ([9.218.2.229]) by ppma21.wdc07v.mail.ibm.com (PPS) with ESMTPS id 4bfeemswjh-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 06 Jan 2026 06:44:10 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay07.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 6066i8uo50987324 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 6 Jan 2026 06:44:09 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E090320040; Tue, 6 Jan 2026 06:44:08 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9153120043; Tue, 6 Jan 2026 06:44:06 +0000 (GMT) Received: from [9.124.214.89] (unknown [9.124.214.89]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 6 Jan 2026 06:44:06 +0000 (GMT) Message-ID: Date: Tue, 6 Jan 2026 12:14:05 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] sched/fair: Change likelyhood of nohz.nr_cpus and do stats update if its due To: K Prateek Nayak Cc: linux-kernel@vger.kernel.org, juri.lelli@redhat.com, vschneid@redhat.com, tglx@linutronix.de, dietmar.eggemann@arm.com, anna-maria@linutronix.de, frederic@kernel.org, wangyang.guo@intel.com, mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org References: <20260102124744.360872-1-sshegde@linux.ibm.com> <20260102124744.360872-3-sshegde@linux.ibm.com> <880e3610-dbdb-42a8-9ddb-ab2e7d3cdc1f@linux.ibm.com> <71485a68-c0b0-446a-8326-7c10c583e076@linux.ibm.com> <7050ce6c-64d6-4359-9a4c-9fd4362e5290@amd.com> <4f3f52ab-b2d5-4c9e-bf9e-94ea75d3dade@linux.ibm.com> <41202126-cf45-46f8-9506-126072bfe0fe@amd.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <41202126-cf45-46f8-9506-126072bfe0fe@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=OdmVzxTY c=1 sm=1 tr=0 ts=695caf3c cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=eJTnxkHzwNBm_rMR:21 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7mrxnKSyDbNkFpouzP4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: s7t8EPwIFu4fLfWgEZ8ppFkrOsWYVOpY X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTA2MDA1MiBTYWx0ZWRfX2krt01rmIqWo imsg7/D4tzfumFiQGSpA76h6z3/himIuTgYRZ/+qK1wHTl7YHwOHrbXwhFS54EaEwE595FEddix q5zy3rwcLP8dDkav55raUVe7vQnEGaSeAVg80VT3doge9Px3YErdNVLJQhAirpSg2VrAA0T4MLu ZHIsOS8gCVQOnIXqViZ+KONvZEh0qJaP578i5YOTDorPrVUwmhP5CmDW0hn/B1Vg8WwuhKuWwpo WlTV6lGQiKwOFuIMAXBSiaLO3Fk+vhCEwQYRSBz15AgiJP4NUsm0jZssCphVTw+/l/56p7TYjMR +EbRgE3GYgGA59Sp8gYoXUJsojvwT/HP1zGA2Om28b5EZQLGQ0xbI7pVMN1G+B3l7N4NqpqxKwd nMYFFBWPfPFW72Mh+gUl0VwlYJADW7rC9ETZFWqWjb+GfS0KsMJ1XNjuGmnIFVZaC5asioelZ9f j7uSMYiE0nJjsSZVFHQ== X-Proofpoint-ORIG-GUID: s7t8EPwIFu4fLfWgEZ8ppFkrOsWYVOpY X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2026-01-05_02,2026-01-05_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 clxscore=1015 phishscore=0 malwarescore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 impostorscore=0 bulkscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2512120000 definitions=main-2601060052 On 1/6/26 11:20 AM, K Prateek Nayak wrote: > Hello Shrikanth, > > On 1/6/2026 9:53 AM, Shrikanth Hegde wrote: >>> There are also nuances like the smp_mb__after_atomic() in >> >> That reminds me, need to upgrade this to smp_mb now, given atomic is gone. > > Isn't cpumask_set_cpu() also an atomic op? > > set_bit() has a comment stating it is a "relaxed atomic operation" in > asm-generic/bitops/instrumented-atomic.h which makes it similar to a > atomic_inc(). " * set_bit - Atomically set a bit in memory * @nr: the bit to set * @addr: the address to start counting from * * This is a relaxed atomic operation (no implied memory barriers). " I believed the comment. If it was relaxed atomic operation then one would need a smp barrier. But it calls arch_set_bit. Looking at x86 implementation in arch/x86/include/asm/bitops.h it looks like it does full smp_mb. Whereas on powerpc it doesn't. So smp_mb__after_atomic can remain as is. Effective change to v3 is return instead of out.