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 EECFD372049 for ; Tue, 12 May 2026 12:25:48 +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=1778588753; cv=none; b=BtlF+366KP67H0LMJZpfzWiRbn/C7b3w4SyiaXmlCF7dCMf64CsHZumpwRp6heWMYPXezb9rMsAMOBkz+SJ9t60ecwaWnuFGF/4kWUA2D5V8YxBOKagqBMc7QstzUx5mcAZWl8pXQ9/BxCteg/VC9lFDtT23C8xAeNRJNuXJnLM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778588753; c=relaxed/simple; bh=FBt51xjUFA0XgEz1j92l0LFlVZcGUowW6AshNwm5LVc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UbKX9zBQpk2T2f7SFLNNTflrM330iaCQarbMMIsXgsxzEzEQ37Rw37JA2Gy+5mpHZQmpPhaLYOOQfAFntOk0wBCRfwhD2aYLIn0od1nBgO4618BZGdhTdPniqb2RPuIdukbc6xNkBsyKCLmEm6WdFIrcur3yvZ4vv4STcv9LT7M= 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=aRgFzKe6; 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="aRgFzKe6" Received: from pps.filterd (m0353729.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 64CBplHl2606373; Tue, 12 May 2026 12:25:22 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=9iHzmc /A6hlb3UVxZ7RxBarUJS6ydhrlCFDZXijEI7I=; b=aRgFzKe6lwSDeJ4EfzPoc0 4uTbG+oIo3BktR3e63j3KpcIONU4pVEZTPwRcg0DjKN86peZSs27F29WmnAvHdqY AeWIN2kVlyDPDnbFmcao5NJQJsKpfj5phHefF7eyOwuUpzbpkvkKevHoLxq1kbt+ 4dCvVCPhZ51w4eBTDsKPLaXjxEXSC+YMQuoSOd8cy2zGi28Ww12cJk/zcxmt8APk T6zcp3/tg7nxezKOuXm2jBS5ZDqG+R1QsDDgmCMtnp50VWymSLO/RpSNznCn7mlp buupK+BdIGrR1g6mPy1XtrqiBZ0buVVCkcP2ZaNj5Bbv1jH7gJTN8H/RLzgOrn3g == Received: from ppma12.dal12v.mail.ibm.com (dc.9e.1632.ip4.static.sl-reverse.com [50.22.158.220]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4e3nv52yds-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 12 May 2026 12:25:22 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 64CCOKjZ015948; Tue, 12 May 2026 12:25:21 GMT Received: from smtprelay06.fra02v.mail.ibm.com ([9.218.2.230]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 4e3nfgb2je-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 12 May 2026 12:25:20 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay06.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 64CCPJpa29753796 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 12 May 2026 12:25:19 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3787F2004E; Tue, 12 May 2026 12:25:19 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E83EE20043; Tue, 12 May 2026 12:25:14 +0000 (GMT) Received: from [9.39.28.106] (unknown [9.39.28.106]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 12 May 2026 12:25:14 +0000 (GMT) Message-ID: Date: Tue, 12 May 2026 17:55:13 +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 0/3] sched: Simplify ifdeffery around CONFIG_SCHED_SMT To: Valentin Schneider , mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org Cc: kprateek.nayak@amd.com, juri.lelli@redhat.com, dietmar.eggemann@arm.com, tj@kernel.org, rostedt@goodmis.org, tglx@kernel.org, mgorman@suse.de, bsegall@google.com, arighi@nvidia.com References: <20260506110052.9974-1-sshegde@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTEyMDEyNSBTYWx0ZWRfX7/hyyYY6kWRc ynLfqTap/OYew/pegMZYj/+rdWHza288oubfdi4JTm04Ia1M/FjgAWpWyegeitFepRqBBuLWoEP r+8S7H8jiptu4cucZ+xXD+MbvoZshQ5g8ZF+KL3yon8saaj4J8y0A4l5APL10HVtKomyhBnHLLY XeOEdbinhDBZm0kVE2cVf4uoqBJ66/QBMjsacYvhx6JaKcO0c4mDuJoKOtSI3rAxYKdXnypaNXI A5q/HYWsyk3QkwRP4VDCkye/tFyg+kRVysLE7tMQmKT7OpX/vVccxX31B/76tVf2EQHiGIsmFrY L8QzUJl5i35CIr3VWn8fZnRqMOFaOrOFaC5ncALYwgLtzKomV3mFtQ+s1tBiLpd27G0b74oQxzh qAsT7AyFNFCjLCl1wu9LVmJKFnoYyekPa0XZRWqzwumpghzkk8t2DuDOeakDm0g84v6KRonU71k LVjrmIEEylq2sL+uKyw== X-Proofpoint-ORIG-GUID: sInhws7uxKSZbpUEfT0kS8wmUL1UJdMd X-Authority-Analysis: v=2.4 cv=Jc6Ma0KV c=1 sm=1 tr=0 ts=6a031c32 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=a8gGu82O-P1m0XLeOPcA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: RrdzWHTPPlaFdfbCmzKV2CKk8dSdqa1S X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-11_05,2026-05-08_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 clxscore=1015 phishscore=0 adultscore=0 lowpriorityscore=0 suspectscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605050000 definitions=main-2605120125 Hi Valentin. On 5/12/26 4:29 PM, Valentin Schneider wrote: > On 06/05/26 16:30, Shrikanth Hegde wrote: >> Plus, Major distros make CONFIG_SCHED_SMT=y for all major >> archs and few archs unconditionally make CONFIG_SCHED_SMT=y (x86, >> s390), So CONFIG_SCHED_SMT=n is a rare case. >> > > That leaves only a handful of #ifdefs: > > include/linux/sched/topology.h:35:2:#ifdef CONFIG_SCHED_SMT > kernel/sched/topology.c:1757:2:#ifdef CONFIG_SCHED_SMT > kernel/sched/topology.c:1802:2:#ifdef CONFIG_SCHED_SMT > arch/powerpc/kernel/smp.c:986:2:#ifdef CONFIG_SCHED_SMT > arch/powerpc/kernel/smp.c:1038:2:#ifdef CONFIG_SCHED_SMT > arch/powerpc/kernel/smp.c:1720:2:#ifdef CONFIG_SCHED_SMT > arch/powerpc/include/asm/smp.h:141:2:#ifdef CONFIG_SCHED_SMT > > The topology code could deal with unconditionally building an SMT layer as > it'll just get degenerated. The powerpc usage is mostly topology and > cpu_smt_mask(). So if we want to push for it, we could even get rid of the > config entirely. > I think that's tricky. This is my take. Feel free to add/correct. 1 - That's policy decision making. It is only scheduler perspective. hardware topology mapping need to necessarily be on the same page. Hence we have the config today. 2 - Implementation is difficult as well. Lets say we define it as: #if !defined(cpu_smt_mask) static inline const struct cpumask *cpu_smt_mask(int cpu) { return topology_sibling_cpumask(cpu); } #endif Then topology_sibling_cpumask could still point to actual HW siblings and SMT domain may not degenerate as it could have more than 1 CPU. And Since powerpc for example defined cpu_smt_mask, will have SMT domain always. That's not correct IMO.