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 4D5E119F464 for ; Tue, 15 Jul 2025 17:04:48 +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=1752599090; cv=none; b=VvD8hNCutT9B7gio8fgLoN2JFo66XQQMraYmnN0p0MpIwrasn+qYC8xmUryt8crYp3AMj+tuCja4VLfaEmStMWSnaJe0VWoSP9eyMLkJ3s3OnITFxcx8W3Lxip+mDtPuhkh5fUnuU4iIsJbi+FhlSatgVlBo8+2l4PZtxlKhRvE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752599090; c=relaxed/simple; bh=3qxGmktSsRF9vQ4LgohfW7cp1sf34H7E1Kn75jahbFk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=A3Gz+doivepkStXc0TUBLVm/11qsz5tBH+q9cgXSH+7Bk2pqxVJ1/dufQEC83Zhwcieg9tToatFk+weHkIo2/lgv3Tnm0x2Rnz0vOqHuS4Y4aTm4OMmOQznHTOozUj0Y+QwGrRDCuUMvf+jXalyfjV0iyu84gAaHDQ6OT4PYp3E= 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=OqP4yE++; 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="OqP4yE++" Received: from pps.filterd (m0353729.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 56FFHFoa027589; Tue, 15 Jul 2025 17:04:31 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=nOl7ms D1HBeiHfswOOmm368DWRfTbx9x2nCdJCDdHY8=; b=OqP4yE++Uji7Zvw5JgLpqI bBKyRYa6csKltR9P3HHWU8GIiecpnLuboM4vmiRddvS2B26wYNqu5TJ8sweAoIMv tOEtGwtO64rTHdgMGREzX0hrOTrX2/sxOBY9jhJBki01UI59PerQNX5sh2SL4kqP 3QCQlYOhgC73kF5B6z9GTvGf6cIOMgvjspgp+FrmMAyGWHk4pbwW0XXjBOKgQLHC 2487pvziU9xGQ/o+P3grMvXHKusu/JzE4kDPd7gd2n753bjHTSHPDYWQgeXEMpps S5G6ULUcTGdotK9Q6lQqcpZzQmnZIgDetuc031yDkMRXWNo57OldMZ/53WHiN+Lg == 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 47vdfmkek2-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 15 Jul 2025 17:04:30 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id 56FG8Oul031985; Tue, 15 Jul 2025 17:04:29 GMT Received: from smtprelay01.fra02v.mail.ibm.com ([9.218.2.227]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 47v21u3nhd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 15 Jul 2025 17:04:29 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay01.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 56FH4SwU46465514 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 15 Jul 2025 17:04:28 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0BADA20040; Tue, 15 Jul 2025 17:04:28 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AC0FD20043; Tue, 15 Jul 2025 17:04:25 +0000 (GMT) Received: from [9.124.217.184] (unknown [9.124.217.184]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 15 Jul 2025 17:04:25 +0000 (GMT) Message-ID: <88edcfdf-2253-4563-a895-6e8bb1625800@linux.ibm.com> Date: Tue, 15 Jul 2025 22:34:24 +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 0/6] futex: Use RCU-based per-CPU reference counting To: Sebastian Andrzej Siewior Cc: Peter Zijlstra , =?UTF-8?Q?Andr=C3=A9_Almeida?= , Darren Hart , Davidlohr Bueso , Ingo Molnar , Juri Lelli , Thomas Gleixner , linux-kernel@vger.kernel.org, Valentin Schneider , Waiman Long References: <20250710110011.384614-1-bigeasy@linutronix.de> <20250715163134.pM1J2XO9@linutronix.de> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <20250715163134.pM1J2XO9@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: yTPuAkgSrMYMKJKd42BTTAfL7UusYFob X-Authority-Analysis: v=2.4 cv=JOI7s9Kb c=1 sm=1 tr=0 ts=68768a1e cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=eVKed6vL87oTk6cZQCQA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: yTPuAkgSrMYMKJKd42BTTAfL7UusYFob X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzE1MDE1NCBTYWx0ZWRfX418sdu+gHd3i YPYEXmAT1d1gAYgCwN+zpSWwF7PP7WDsH+Ri+fCJAqEzpUHPIjuwK3byQWXwZdNK8ZcZ/NZW5M/ UOQ+HBoJfXLGkOrwFTtqvgfdd7yOY4Ql3X6GeRL+WN0ZQ/E7KPLZi9jfVu5xJvPyNzFW3K69KLv E77xjIPsRE8/OAMi1oDx+QRfMeOM+8Z0jv6ZuNF5ajLRnEbOlkUOJLiOqKdYyLc5g++R/9Sf8UF kKq7SG8iLozbn3nLaSxtX87zj5eFS2NtREH1i2eV8OWP5vY2dyPaV0sl8rCwN46c8te3mslFTG+ C5o896a+ah7LrkQygE28Phx/Pw22B+0pnyY288s2oGaQvQZ5FKYeOv8Z9SIJRQKss0Th92pvRiY mr2DPkpU7g7s1Ko3DixG43qBqG9X4w0YXbGV+5oZxo9fTGy4ov9ftCbOZ4KfkTZTgWrIodYG X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-07-15_04,2025-07-15_02,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 phishscore=0 mlxlogscore=800 malwarescore=0 clxscore=1015 bulkscore=0 priorityscore=1501 mlxscore=0 spamscore=0 adultscore=0 impostorscore=0 suspectscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2507150154 On 7/15/25 22:01, Sebastian Andrzej Siewior wrote: > On 2025-07-15 21:29:34 [+0530], Shrikanth Hegde wrote: >> Hi. Sorry for not stumble upon this earlier. Saw these now. >> >> Since perf bench had shown a significant regression last time around, and >> for which immutable option was added, gave perf futex a try again. >> >> Below are the results: Ran on 5 core LPAR(VM) on power. perf was compiled from tools/perf. > Thank you. > > If you use perf-bench with -b then the buckets are applied > "immediately". It mostly works also with auto scaling. The problem is > that perf creates the threads and immediately after it starts the test. > While the RCU kicks in shortly after there is no transition happening > until after all the test completes/ the threads terminate. The reason is > that several private-hash references are in use because a some threads > are always in the futex() syscall. > > It would require something like commit > a255b78d14324 ("selftests/futex: Adapt the private hash test to RCU related changes") > > to have this transition before the test starts. > Your schbench seems not affected? Yes. schbench shows similar number. > > If you use -b, is it better than or equal compared to the immutable > option? This isn't quite clear. > n I did try again by going to baseline, removed BROKEN and ran below. Which gives us immutable numbers. ./perf bench futex hash -Ib512 Averaged 1536035 operations/sec (+- 0.11%), total secs = 10 Futex hashing: 512 hash buckets (immutable) So, with -b 512 option, it is around 8-10% less compared to immutable.