From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3A3E5C531D0 for ; Mon, 27 Jul 2026 04:19:10 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4h7lj80Lnmz2y1F; Mon, 27 Jul 2026 14:19:08 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=148.163.158.5 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1785125947; cv=none; b=XpjGE3WDNHDz/FnrSi1GNQQ+7aAoLy55R3bHYPZQuHdT92+b+s/b4t+2S1+WtlLd+VxU1F7OAHBiCvX6y17sqE3V/P56li/t+jdYxaoN0ZHhg5YstoE42Tc/+gAvL6/lZU6sF5AP0+EiuLD/VMpimBquZ7Fe4Q1VSlVhpPcCdTkZZ+qEezZUJGZTs6XD4i1uHOSWfF4/Jo2+m6ZRaKdLN4A+EbxPpg+xxyFI5DJpZez919R5eDzpz+iXjPuohnRPuRLmmOAgQwUVeBeyD1VXU+FnWvWpzZQVg2ZPx1hgerBjhNQefGCMWNis8RlaJgcXoRSrw+kuHWTxFmCpY5Ns0Q== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1785125947; c=relaxed/relaxed; bh=s+e7jkFKJSm7jW1mU0dq9zB64RdZT8FHKFStWfM48sw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aRze9EYd9mZBKh5ZnOe/OtvFnsGfrx7HnnzSx6BLgvxDn0HXGmRVT52ybd3nMtbsYjIKJt4d8DPxrkjkKi5um7BQf9/npD4tCU506roKdn6xynLIr5649XZtkuEl4t+KX1SQdTop6kWDd3F73Pzrzsb4AUAOGFFJkVlSw8x4GX+XUEnguq1XzMuHxjhC5tet/R+GhOR8zcU63gVo+XqbEo7qpHIJoCIWg9LXT2Ry2bTKR/4tAQVGa9zU/gS6HjX5YmM3CtJ3tudlWdcFbS5RYRTURw86ScsC7KGVW5bWoIAkWLYGzBoG8w0FMLCy2UvN08zXQIUU+ZMPFC7QPfPoUw== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; dkim=pass (2048-bit key; unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256 header.s=pp1 header.b=o4qgM4Mx; dkim-atps=neutral; spf=pass (client-ip=148.163.158.5; helo=mx0b-001b2d01.pphosted.com; envelope-from=sshegde@linux.ibm.com; receiver=lists.ozlabs.org) smtp.mailfrom=linux.ibm.com Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256 header.s=pp1 header.b=o4qgM4Mx; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.ibm.com (client-ip=148.163.158.5; helo=mx0b-001b2d01.pphosted.com; envelope-from=sshegde@linux.ibm.com; receiver=lists.ozlabs.org) Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4h7lj71Xqxz2xKh for ; Mon, 27 Jul 2026 14:19:06 +1000 (AEST) Received: from pps.filterd (m0353725.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 66R1lmfF769497; Mon, 27 Jul 2026 04:18:33 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=s+e7jk FKJSm7jW1mU0dq9zB64RdZT8FHKFStWfM48sw=; b=o4qgM4Mx/VXZYdgKgoqdBA 6IH3WPb9v09SEvxvQaNzQv9c1CVYoWN3JT0qaxjWbQa5Sxi0LzP79E/s1d33cgSX mvI70syOqOzddVxKrW/IqLoTZlWUAsDYir1RKpbREV3gfyWsDWAPtwYlxIetoA0q m9NkuCKFCYEVpCpJ5k/qOQfcEJwEKZVnEGqu9exOhksapsz6WCZkEGkzoK4tLZcs upHmneBFs/RPvCnMuRLO7/vZatiYd5dCNBYVnfCvHr7Zna8TSKkKWPH4MDL/eaku iFZpcvesh8RLefLKDhWMcc5AbTxT0hvke9/fUuhTR2hLfpVo5Et8LMemoHFjgc2g == 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 4fmv0ndpg6-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 27 Jul 2026 04:18:32 +0000 (GMT) Received: from pps.filterd (ppma21.wdc07v.mail.ibm.com [127.0.0.1]) by ppma21.wdc07v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 66R4BPhT024341; Mon, 27 Jul 2026 04:18:31 GMT Received: from smtprelay04.fra02v.mail.ibm.com ([9.218.2.228]) by ppma21.wdc07v.mail.ibm.com (PPS) with ESMTPS id 4fn8fjuu8p-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 27 Jul 2026 04:18:31 +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 66R4ITBO12517774 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 27 Jul 2026 04:18:29 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 70DED2006E; Mon, 27 Jul 2026 04:18:29 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id F1B182006C; Mon, 27 Jul 2026 04:18:26 +0000 (GMT) Received: from [9.39.23.10] (unknown [9.39.23.10]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 27 Jul 2026 04:18:26 +0000 (GMT) Message-ID: Date: Mon, 27 Jul 2026 09:48:25 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/1] powerpc: enable dynamic preemption To: Jirka Hladky Cc: maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, christophe.leroy@csgroup.eu, mpe@ellerman.id.au, npiggin@gmail.com, bigeasy@linutronix.de, will@kernel.org, linux-kernel@vger.kernel.org, "Paul E . McKenney" References: <20250210184334.567383-1-sshegde@linux.ibm.com> <20250210184334.567383-2-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-Info: AW1haW4tMjYwNzI3MDAzOSBTYWx0ZWRfX0dyuVLO7WMA6 waj8ATPcBTCocJ4/0195AvdHHf/7CGCoBEgsPOhfd2aquSKMpxQQF8Bf0LocLZ5TzPkalAa/mCn nuhJiZ9hVCr4TCp0VMdKCUhM1Gh3OlE= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzI3MDAzOSBTYWx0ZWRfX5Syog1p798Je Wj6X8JEm40AahqWASLaPg2OrIxw4OAhi6upIg4Y9siDCKbK3W9Evn9ej+n2yUAbj8kNla6tizpI 2zXJWcwMRWwKgdZlHxSLsalSzBxE98NSWzEax3znGfjaTAnI6ktMM5HXgQ1dCFd6R9cr9tJ1Ynn tYyww+mNMmgYVmBfec2EiAiWMmoTU/phL8GoCXojNyxA9LIuapFjf4wztLvQ6uuMs50ma5rbBVd IQApIw/AcK1V2QcNG6WLFr2gu+2xJ6bnrXuCJtu4GqkyLsfquI8xnnXud2sF8p7xKDGfCHn4aAh 4cEW+ZivGZcNE8ATwxzuIvjsws7hAOc7cCxuFCl0VVyfzrwzl0nG4lggp2TyRc+wnt2QBz3T7qC ROT8yLGBSWcxbDztmXyTlAdgDdxXXIHOAWmDt4TvNyqwY4ErLmUbWfDy5gnYjQHWimCuJKKeLAK UgzbvQUISBnZFydX+wA== X-Authority-Analysis: v=2.4 cv=b5WCJNGx c=1 sm=1 tr=0 ts=6a66dc18 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=WCvXFVo8NGMObP1iTCQA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: Y7O2bbFrWB8ZbNPYQkJ4CreFfKHts4oh X-Proofpoint-ORIG-GUID: V0sD5WmVoqZRmlE5UDM33GA9tPAK-UOA 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=2026-07-27_01,2026-07-24_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 adultscore=0 malwarescore=0 impostorscore=0 bulkscore=0 phishscore=0 suspectscore=0 clxscore=1011 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607270039 +cc paul for any further/RCU insights. On 7/27/26 12:03 AM, Jirka Hladky wrote: > Hi Shrikanth, Christophe, > Hi Jirka, thanks for the report. > I'm seeing a significant performance regression on ppc64le after this > patch landed in 6.16, caused by CONFIG_PREEMPT_RCU becoming active > once HAVE_PREEMPT_DYNAMIC_KEY is selected. > This is true only if user selected PREEMPT_DYNAMIC option i think. config PREEMPT_RCU bool default y if (PREEMPT || PREEMPT_RT || PREEMPT_DYNAMIC) select TREE_RCU > Benchmark: stress-ng kill stressor (tight kill() syscall loop), > single thread, POWER10 LPAR (8 vCPUs, 1 core SMT-8). > > Bisected across Fedora ELN kernel builds on ppc64le: > > kernel CONFIG_PREEMPT_RCU kill bogo-ops/sec > --- 6.15-rc6 (eln148) no 103,207 > 6.16 (eln150) yes 70,281 (-32%) > 6.18 (eln154) yes 72,552 (-30%) > Does your preemption mode remain the same in two cases? > For comparison, x86_64 (AMD EPYC 9355P) with the same config change > shows only a 2.8% regression: > > 6.12 x86_64 37,436 > 7.2 x86_64 36,392 (-2.8%) > > perf report shows the overhead comes from rcu_read_lock/unlock in the > SELinux AVC path (check_kill_permission -> security_task_kill -> > selinux_task_kill -> avc_has_perm -> avc_lookup): > > Function 6.15 (no PREEMPT_RCU) 6.16 (PREEMPT_RCU) > --- avc_lookup 15.23% 24.79% > __rcu_read_lock ~0% 4.52% > __rcu_read_unlock ~0% 4.17% > selinux_task_kill 6.23% 7.35% > audit_signal_info* 0.94% 3.59% > > On x86_64, rcu_read_lock/unlock are cheap thanks to static calls > (HAVE_PREEMPT_DYNAMIC_CALL). On ppc64le with the KEY-based > implementation, the weak memory model requires real barriers > (lwsync/isync) making each RCU read-side critical section > significantly more expensive. Weak memory model would need barriers irrespective of HAVE_PREEMPT_DYNAMIC_CALL or HAVE_PREEMPT_DYNAMIC_KEY. That's my assumption. I will look more into it. Also i don't know much about PREEMPT_RCU. So might take a while. > > This aligns with Christophe's earlier review comment that > HAVE_PREEMPT_DYNAMIC_CALL should be more performant. Would > implementing static calls for ppc64 be feasible to close this gap? > Static key too is expected to minimal cost. There maybe more into this. > Test details: > - Machine: IBM POWER10 (pvr 0080 0200), pHyp virtualization > - stress-ng 0.21.03, gcc 14.3.1, glibc 2.39 > - Tuned profile: virtual-guest > - SELinux: enforcing (permissive recovers only ~7%) > > Happy to run additional tests if needed. > >