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 9A6AF3D34B7 for ; Thu, 19 Mar 2026 13:25:22 +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=1773926723; cv=none; b=XMdA8vZ7eSXGLJQ586JM/Edy3fv1Zgq7pymtplVPFDLsRy5iolngwKIYEQqw2jV6KR8t9knTTXhq2pkrOr4OIyRhmQAFmf5//qRyUGTDCUpmR5cImuBa7m1boAtHzjLCJoo3Mva+Ee3PhHZ336vQveFeSFmnPwiCoXwlDU+GANg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773926723; c=relaxed/simple; bh=ySyOU+m8fXKS8aJzHZd1c+iDBPas6AzfR+SvuynM+II=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=htAZDM6IbC/r9wQqVJbVrupoCLL94XnonW5/aIU1ZuW7uqqo7Xt1KnEUZ8glINPNG4PBzA0bcjp9Bkm4CFL1qWCUcDQ/zdPJtrEsN07ijxF+//Qry0yPfodSNRnegiCYCMgfYGGJtqjvpZevJvtzWIR7j2EA0IhHLy/qo/t9Z4c= 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=bEiWb/7v; 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="bEiWb/7v" Received: from pps.filterd (m0360083.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 62J736db3456305; Thu, 19 Mar 2026 13:03:25 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=up6J4a Eq3c8/yB84CWzz7qbp4nKv63Zal5nYG9iyzqg=; b=bEiWb/7v2cp/klEGME7Wq5 14DK/FPcBe3sn3cqSXrhIuTafBLpQJ6agc0Nz/0AWMaIw0NwbqqoONOMiifWaZir B3qOSBJkRYBRZwe+wRQE1RmvAz/Z2IilR2RAdhS6bzB0u4VPJHiXXKi7oegHVXoM OxHiqJoB37BxOOzb/pcWUkiqxGIIItUNB9oSrQlFAz9VYNjt0XINu8hKmBlQ5vID qovhcG+EU46yl/ZRoZhjiFJbASTJoX3nzpOQRwy7/9M+bcm13RHyH2oHNqi2ZU2R sGKujCecWq5spQQaDbTAIcm3YaCMGwmcV5GNJXCvyqeOTFk5Ali+ERSZUOQmHlSQ == 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 4cvy64y3gn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 19 Mar 2026 13:03:25 +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 62JAWn5B032333; Thu, 19 Mar 2026 13:03:24 GMT Received: from smtprelay02.fra02v.mail.ibm.com ([9.218.2.226]) by ppma13.dal12v.mail.ibm.com (PPS) with ESMTPS id 4cwm7k2brh-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 19 Mar 2026 13:03:24 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay02.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 62JD3Md152625778 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 19 Mar 2026 13:03:22 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6E14020040; Thu, 19 Mar 2026 13:03:22 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 82E0920063; Thu, 19 Mar 2026 13:03:20 +0000 (GMT) Received: from [9.124.220.229] (unknown [9.124.220.229]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 19 Mar 2026 13:03:20 +0000 (GMT) Message-ID: <5a7b737b-ecae-4dad-9965-5297991c01bb@linux.ibm.com> Date: Thu, 19 Mar 2026 18:33:19 +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 2/2] sched/fair: get this cpu once in find_new_ilb To: Peter Zijlstra Cc: mingo@kernel.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, kprateek.nayak@amd.com, juri.lelli@redhat.com, vschneid@redhat.com, tglx@linutronix.de, dietmar.eggemann@arm.com, frederic@kernel.org, longman@redhat.com References: <20260319065314.343932-1-sshegde@linux.ibm.com> <20260319065314.343932-3-sshegde@linux.ibm.com> <20260319092030.GU3738010@noisy.programming.kicks-ass.net> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <20260319092030.GU3738010@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 6YnbXNlM_LmbNYSTkpUEz4jd8l23R_gj X-Proofpoint-GUID: 6YnbXNlM_LmbNYSTkpUEz4jd8l23R_gj X-Authority-Analysis: v=2.4 cv=KYnfcAYD c=1 sm=1 tr=0 ts=69bbf41d cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=1lkx5Zz7rA4iFeylUhIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE5MDEwMCBTYWx0ZWRfXxoM0LjqF6BFW WKP2IbozybnkqdxQcTCoopMwZEdNOCgyqudHhV5DVsbpEPv+AxzQGAFpOpNvOX9BmxepWZVsi0O EWpRGNm3Qi/NMhcErCYJHIecIVmN9Yi9FGI//Lmdj0tSD+dq+Ait1/B/fifm4A/9dWUC9SipnPq J0VWcQk3PlJOZ4LnKZtHmisM0kwu9V8NmDEctyx149x6yOI2mlm3zlepCREtn0D2SUtdfCHnBvs jMxxZ8Y+hkBdYzxHVj53iZeAdlrhsh1fJmW+i+lX5dVYJp3boVi5o8k+a1t6WzusUf2Rns0/9rL W5tnA7NkEQvcjgyeUakaJ0K2fMoTjBEDwyEwFc/3bXX64AIk13BpNLaE3pkpErUw43cHcQCpigb yxfyrOsVQ2Txjt+zHj7o023S19IHX+gmXZu/wl8QMdM0XFDEti86XDQZ8ka6XBADQMWkBgNq9uT 2nJirdw02G7+n4coCEw== 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=2026-03-19_01,2026-03-19_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 spamscore=0 impostorscore=0 malwarescore=0 adultscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603190100 Hi Peter. On 3/19/26 2:50 PM, Peter Zijlstra wrote: > On Thu, Mar 19, 2026 at 12:23:14PM +0530, Shrikanth Hegde wrote: >> smp_processor_id() is pointless to fetch in the loop. Move it out. >> No functional change. > > Isn't this what compilers are for? This is what i see in pseries. c00000000028cc7c: 1d 70 80 48 bl c000000000a93c98 <_find_next_and_bit> c00000000028cc80: 00 00 00 60 nop c00000000028cc84: 00 00 bd 80 lwz r5,0(r29) c00000000028cc88: b4 07 7e 7c extsw r30,r3 c00000000028cc8c: 78 1b 7f 7c mr r31,r3 << This is ilb_cpu c00000000028cc90: 78 1b 7a 7c mr r26,r3 c00000000028cc94: 40 18 05 7c cmplw r5,r3 c00000000028cc98: 78 f3 c3 7f mr r3,r30 c00000000028cc9c: 5c 00 81 40 ble c00000000028ccf8 c00000000028cca0: 08 00 2d a1 lhz r9,8(r13) << cpu comes from paca_index c00000000028cca4: 00 f8 09 7c cmpw r9,r31 c00000000028cca8: 18 00 82 41 beq c00000000028ccc0 c00000000028ccac: 8d 0c 04 48 bl c0000000002cd938 c00000000028ccb0: 00 00 00 60 nop c00000000028ccb4: 00 00 03 2c cmpwi r3,0 c00000000028ccb8: 78 00 82 40 bne c00000000028cd30 c00000000028ccbc: 00 00 bd 80 lwz r5,0(r29) c00000000028ccc0: 01 00 df 38 addi r6,r31,1 c00000000028ccc4: 20 00 a5 78 clrldi r5,r5,32 c00000000028ccc8: 78 e3 84 7f mr r4,r28 c00000000028cccc: 78 db 63 7f mr r3,r27 c00000000028ccd0: b4 07 c6 7c extsw r6,r6 c00000000028ccd4: c5 6f 80 48 bl c000000000a93c98 <_find_next_and_bit> So, yes it is done inside the loop. But accessing it should be cheap as it is r13 access which is the paca pointer. Since different archs implement it in their own ways (many would have it cheap, but for some may be costly) and there is CONFIG_DEBUG_PREEMPT too. So it would be good to hoist it out of the loop IMHO.