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 BA70B38E8BA for ; Fri, 31 Jul 2026 08:03:16 +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=1785484998; cv=none; b=FkrYpNdJnmPhRJ2OOKOPg/P53XDkTnh8PLDlG+E1gxj3h/xn7t32X+ez/e3901L7N1e88tYE/pS5trALaavf6COdizu7zmLTK9iC4RUEJNgpQt8BJ4n/WDWXsvaYHy1NZ7PqeLrF85k2TXWuFauFW84GRde/hBW5qk3d7+TzmAM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785484998; c=relaxed/simple; bh=CY4Bq2mi1FGLvR1u5U8fIU85Ism5Q12s2yg+x4kyHU8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XY/3J73tteSFW2ufez8aRD4KQjyFhUp6Io0xQl+jlU054LIsdNEoUXmSCx5NMviZDFn6PT4at2G8Y9qcKDy3tx0WKFlw975AWk/Wa9js+idvQl6TnTDlhcZJ/y+hQpLJsKvHHS1lB2JKBSubi22Ve0wTJx4K6oXA3hpfapUMWI0= 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=Y83WawHl; 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="Y83WawHl" 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 66V5IC5Z3253837; Fri, 31 Jul 2026 08:02:34 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=djgo2j g+/VqHj2o+e2CqLoyQfJPLpcK3m4va8704NHE=; b=Y83WawHld0AW23qHLcG3W3 7uC1PYeCMnMDqs1OvGAMLmEmdRRMj3JDVs+5NlALJtPTrm37cG+ZicBtmmqvw4bb Pch3RnOqArMdKzqUm6DPrlQ7VXH0MZBPowPH/2AT+zK7SSSLhW+f6nvUwYwmfn93 nX3h5Z8xXr4HEa9ijJoIxqjgTpBaTY2gZcVHUn7W7s9bHegjkPpBk3dPsY8j0cTV 6+D93u5W4mn+MxANDjtBmTfBhwnhI9P7hpBE0QHadgBaoJ/sTHetO9gRtL0Ub+65 0u9ArgdU3haIZnOH7x6Tb8iKhnCgiih050aKCvWACROzOCKS7H+UQpiNFMEhujIw == 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 4fmuycuwt9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 31 Jul 2026 08:02:33 +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 66V7v4Rg001445; Fri, 31 Jul 2026 08:02:32 GMT Received: from smtprelay04.fra02v.mail.ibm.com ([9.218.2.228]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 4fn7fqq7ha-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 31 Jul 2026 08:02:32 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay04.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 66V82UkB15991246 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 31 Jul 2026 08:02:31 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D52FB20043; Fri, 31 Jul 2026 08:02:30 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 41C5B20040; Fri, 31 Jul 2026 08:02:28 +0000 (GMT) Received: from [9.124.209.55] (unknown [9.124.209.55]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 31 Jul 2026 08:02:28 +0000 (GMT) Message-ID: <4be922b5-7dc2-48c1-938c-de02245bc5e2@linux.ibm.com> Date: Fri, 31 Jul 2026 13:32:27 +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 v4 1/1] powerpc: enable dynamic preemption To: Jirka Hladky , "Christophe Leroy (CS GROUP)" Cc: paulmck@kernel.org, maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au, npiggin@gmail.com, bigeasy@linutronix.de, will@kernel.org, linux-kernel@vger.kernel.org References: <500d8e8c-088c-4e6d-ab53-868ade6b0eda@paulmck-laptop> <29a407ab-268e-4443-96dc-8f5f933cb63c@linux.ibm.com> <529b8d9f-54a0-4ec2-9886-83cd528e5e04@paulmck-laptop> <57d9de4a-65aa-44cf-9024-de4e5bdd1971@linux.ibm.com> <972db4f1-406b-477b-895e-59ffc643e384@kernel.org> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: Zzv-a9yxYUjkVjkt7e82Si-Z1YAjT8bk X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzMxMDA1NSBTYWx0ZWRfX56C9ifWkB6d2 qlmsMGT+at9af0Yrfj8xN+ZNI+9mo9oUBBHnSnKtC6mIc3peHc/u7VRDWQfazC5yXIDBULOVmP2 r6DDTM+54B71ZYsok8t4S6+DZB/Lw6/U7tYtOMHaaZsJ15nLfJzvfZxsFGaafpycc/kLKeTqn1R NJWGkrH76Q+xs7Iuw0QWwqUYk+Y6n0G9bAFQkwQBxD1/gmMBIWLWVdSaEEBJk9iakcQUnjxCUOC V9liD6DmltNNdobN6ei4/ldNyXlcp39DbxNlNpVlqSVEpq8Hw7om4zmzfIm6miz+Tbxo5J7Z2qG Qs1H1H6yiMmli0svTHFWd+W2/NHJHY/6zLvhigbsFRBLtXqpJ2QRXrcBl+kT57JtxfC84e0U/Km nSeWXtjmBjT1I+ZsoELxxeWfIVm8KhqqQy3z8F8BXqF/lEZswgj0arC245RVrsk3aIz+Pw0fs57 mDfW02RC7BzsdPIZJzg== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzMxMDA1NSBTYWx0ZWRfXzh6cY7XkKGu4 Ums9z9K38kSh+ieShXdQ8WHfvSlsd0jF9n7Vx3BpnfyviJFCX1ZzRfUA6m9jU5MtAgdoh78J1II wYUmgp02vEc9OZpR1eZWkU3htMDwDHo= X-Authority-Analysis: v=2.4 cv=AZeB2XXG c=1 sm=1 tr=0 ts=6a6c569a cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VwQbUJbxAAAA:8 a=oHPdpl245dM498GvQYYA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: NYe4f62dOEyqXzb4Lte0WSUnzbpKS-5v X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-31_02,2026-07-30_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 priorityscore=1501 phishscore=0 adultscore=0 impostorscore=0 clxscore=1015 malwarescore=0 suspectscore=0 lowpriorityscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607310055 Hi. On 7/31/26 12:48 PM, Jirka Hladky wrote: > On Fri, Jul 31, 2026 at 7:03 AM Christophe Leroy (CS GROUP) > wrote: >> >> >> >> Le 30/07/2026 à 19:10, Shrikanth Hegde a écrit : >>> Hi Jirka, Paul, >>> >>> >>> +cc will >>> >>> On 7/30/26 8:38 PM, Jirka Hladky wrote: >>>> On Thu, Jul 30, 2026 at 4:53 PM Paul E. McKenney >>>> wrote: >>>>> But is this really a fundamental RISC cost? For example, does arm64 >>>>> see the same performance issues? >>>> >>>> We tested arm64 (Ampere Altra Max) with the same controlled >>>> experiment -- two 6.18 kernels, both voluntary, differing only in >>>> PREEMPT_DYNAMIC: >>>> >>>> Arch PREEMPT_DYNAMIC kill bogo-ops/sec Delta >>>> ------- --------------- ----------------- ----- >>>> ppc64le off 108,836 >>>> ppc64le on 68,197 -37.3% >>>> aarch64 off 5,538 >>>> aarch64 on 5,082 -8.2% >>>> >>>> arm64 sees -8.2% vs ppc64le's -37.3%. So arm64 is affected but >>>> much less severely. >>> >>> Ouch!. But that's good to know. >> >> Might be a stupid question, but what is your .config ? >> Are you sure it doesn't contain CONFIG_DEBUG_PREEMPT ? > > I have double-checked that and it's not set: > # CONFIG_DEBUG_PREEMPT is not set > > Thanks > Jirka > Coming into numbers, I did notice later, arm64 numbers are almost 20x less. I believe you are having similar core count or benchmark is same. But if we compare the time taken for each operations, it tells a different story. PREEMPT_DYNAMIC ppc64le off 108836 ops/s = 9.19 us/op ppc64le on 68197 ops/s = 14.66 us/op delta +5.47 us/op aarch64 off 5538 ops/s = 180.57 us/op aarch64 on 5082 ops/s = 196.77 us/op delta +16.20 us/op PS: I tried porting some of those changes in arm64 to powerpc to split preempt count into two. but i don;t see much improvement there. If i see get better numbers i will reply with that.