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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by DS1PEPF00017097.mail.protection.outlook.com (10.167.18.101) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8445.10 via Frontend Transport; Sun, 9 Feb 2025 23:39:20 +0000 Received: from [172.31.188.187] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Sun, 9 Feb 2025 17:39:15 -0600 Message-ID: Date: Mon, 10 Feb 2025 05:09:12 +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 1/2] pipe: change pipe_write() to never add a zero-sized buffer To: Oleg Nesterov CC: Christian Brauner , Jeff Layton , David Howells , "Gautham R. Shenoy" , Mateusz Guzik , Neeraj Upadhyay , Oliver Sang , "Swapnil Sapkal" , WangYuli , , , "Linus Torvalds" References: <20250209150718.GA17013@redhat.com> <20250209150749.GA16999@redhat.com> <20250209180214.GA23386@redhat.com> <20250209184427.GA27435@redhat.com> <20250209191510.GB27435@redhat.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20250209191510.GB27435@redhat.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS1PEPF00017097:EE_|PH7PR12MB8793:EE_ X-MS-Office365-Filtering-Correlation-Id: 7d3bfcfc-782a-4514-1acb-08dd4962f9bc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|82310400026|36860700013|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?MVU3azhpSzZIWGJzMzJpRVUvVEo1dlVQWjJoNTcyWkxMRExlT0kwdEpCbTF1?= =?utf-8?B?aTR2dGtTN0dvOEpEcEJBamVRZ3VNVjltR2ZNZ2hHMlVsMjdUT2N1d1QvZncy?= =?utf-8?B?UTh2R3hvZWRYR1d4ZkQwZDJWVGtrZmxENFc3MS9KQloybHMvVlBOU2dwZzQx?= =?utf-8?B?Zm9RNVg2MlRrTFNjbnFiOW80aVJLeTl4OEVna3lsLzlmREw4TTZzZGl1akNM?= =?utf-8?B?bWtKRDY0cVgwaUJqL2doQ2FxWEk1S2FHU3RUUWhKTlM2cWpqTEt4MWhpZExH?= =?utf-8?B?RThWWVVOeGtiVngvdHk0a2phWHlUcUFFdnBOMTJPT1RXNHppd3VVMXV3emla?= =?utf-8?B?S3FJRjk4QTk1WFZjSWFaWC9rbngwRW5WNmt3M1NoWDVvSUFaNEFOdGtQdDlr?= =?utf-8?B?UUlyS0N1VkQ3WFo5bUZ1ZnA1UGgrN2c3eTNzNTRTclljSjExYlJPWTRCZE9l?= =?utf-8?B?VUFMQmdVOUcwTlpIQXQvSENKTzRuMXNrTDN4aDVOYU1XVXpSWFFwaDBWdnZa?= =?utf-8?B?b3BmaE1kbG1lK29SNGV5b1dUcm52Y2IvV0txc3RmaTNVS2pyQm1TMWp4L1d5?= =?utf-8?B?REpTRHB1OXdMVlFCL3ozaFpqQUtTTnlQM21Cc1NhTWNabG1CWE1KVWt6S29n?= =?utf-8?B?NjZlRnZuZ2QxVHQzT25CamxNQUZxTDFlenhMVjR4VEJjZm9CSUo5ME8wcm1h?= =?utf-8?B?KzJtZ2JKdFRWWkVYdmNYOFN1NkJna0FMdG5Oc3pGOXdRTmxReUVZbWprdXJ1?= =?utf-8?B?YU9YeDRTMm9ZWjFadlI0b2V0SkNoTXJKUnZOU1k1ckxoOHF2RzBzaHZicmtN?= =?utf-8?B?cHFzT2RmNUtBcS9uN1FOdVlqT1UwUHBnL2JrTnNLVk1JWFJPSHh1ZENES0pX?= =?utf-8?B?OUtHMDA0dUV2THVkWDU3Nnd3NVFOazA2a1pVZkRKNTZpcTF6bk1OcE1JcTB6?= =?utf-8?B?WE0vbWFRblMxWXJQcVU1a2tGckFjcmFVL2Y2RFVySFZDZHJ0TzZTMWRsRU95?= =?utf-8?B?eHJ5SzJ0czlibmh6bStMM0dWbzRzNTVTQ09HWTdkWnNjWkljTFRZSGtCeHp5?= =?utf-8?B?Z1krNFFrRE5aakxRa0VlOHNMWVFOKzFLQ09WL3BkTU9TMEZzaEdFRGxWUk81?= =?utf-8?B?RFZtS1B1SUNhOUdYU2RDL2xESFI3RVhkd1VJOW9BRVQ4U3NvcHE5eThVWVJh?= =?utf-8?B?NXY1cm5TR2ZWTCtsUGNKSktLQ2FQR3Y5NElwM0VsV0ZlOUowa0J3bStTaGxk?= =?utf-8?B?dU9sZk5JZDdpbHdHSVJQQW9ZSWpJY2NhZ2RVdE8zMVVVRG1rd2ZITHgrWG5E?= =?utf-8?B?d0FHRnBmTUdybnByNjMvaitLN01kQU02ZzFhRi9Telo3Q2pKVlpzTFlJOUtI?= =?utf-8?B?ZjVUN05md0xFT3NTdHl3OFJzdWVzNm9FN1FidGJBaGF4NDZOait0NlJ0RDFB?= =?utf-8?B?Ni9ybVQ0aUMrdXU5S0tjeTIxaDQzQmk1M2dsRFlWUnk0a3pkMk9uSll1c0lM?= =?utf-8?B?c0ZZdWdMaGFBcTBEdmRFN3FPVkZVazJzUDZJQUNzUGpEdUVxeHZ1a0hTL0d5?= =?utf-8?B?aDU2SFJKRVc3bHN6L2ZCaVlaZjdUZmtkT2hoT0tpTmNKZkR4djhvYXdCci9P?= =?utf-8?B?aE5aNWdTeW1zeEJLa3pEMk04TXBvV2ViK0pRVk1lNlNFL0I5Nkl6eC8xc3lK?= =?utf-8?B?SC9hZmdzcE1VQmNXOHlzbFp0bmNFUmNyQitTMU9nL09wODhtUzNDbU4vVnNO?= =?utf-8?B?aDFTZ25XaTlDYUpFWXcwUFpmNUFDWWM4a3JkZ09GVmRXMTVvdTdXR2YxMEJF?= =?utf-8?B?MGFWQmpzOUJkRGwzYnZOY29PbmpYUXlCbXlwQVY0NWhuelBmK1FmNmI2aUJx?= =?utf-8?B?Y213QlVhUHYyZHR6SzNsQVVvQjhxdmRTZzdqY2R5c2lHTms2ZWc5cmY4c2RE?= =?utf-8?B?WHJxOUxpdEFqN0VnNVBQMWhDalJnNjAwdnBnNkFWR2Ntc0tLMzlqakhNNi8w?= =?utf-8?Q?bEFnB21H0aYGPWY0Z0Uff/UrEYgEiE=3D?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(1800799024)(376014)(7416014)(82310400026)(36860700013)(7053199007);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Feb 2025 23:39:20.0861 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7d3bfcfc-782a-4514-1acb-08dd4962f9bc X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: DS1PEPF00017097.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB8793 Hello Oleg, On 2/10/2025 12:45 AM, Oleg Nesterov wrote: > On 02/09, Linus Torvalds wrote: >> >> On Sun, 9 Feb 2025 at 10:45, Oleg Nesterov wrote: >>> >>> Again, lets look eat_empty_buffer(). >>> >>> The comment says "maybe it's empty" but how/why can this happen ? >> >> WHY DO YOU CARE? > > Because it looks unclear/confusing, and I think it can confuse other > readers of this code. Especially after 1/2. > >> So here's the deal: either you > ... >> (b) you DON'T convince yourself that that is true, and you leave >> eat_empty_buffer() alone. > > Yes, I failed to convince myself that fs/splice.c can never add an > empty bufer. Although it seems to me it should not. > >> In contrast, the "eat_empty_buffer()" case just saying "if it's an >> empty buffer, it doesn't satisfy my needs, so I'll just release the >> empty buffer and go on". > > ... without wakeup_pipe_writers(). > > OK, nevermind, I see your point even if I do not 100% agree. > > I'll send v2 without WARN_ON() and without 2/2. Went ahead and tested that version on top of mainline with your previous change to skip updating {a,c,m}time, here are the results: ================================================================== Test : sched-messaging Units : Normalized time in seconds Interpretation: Lower is better Statistic : AMean ================================================================== Case: mainline + no-acm_time[pct imp](CV) patched[pct imp](CV) 1-groups 1.00 [ -0.00]( 7.19) 0.95 [ 4.90](12.39) 2-groups 1.00 [ -0.00]( 3.54) 1.02 [ -1.92]( 6.55) 4-groups 1.00 [ -0.00]( 2.78) 1.01 [ -0.85]( 2.18) 8-groups 1.00 [ -0.00]( 1.04) 0.99 [ 0.63]( 0.77) 16-groups 1.00 [ -0.00]( 1.02) 1.00 [ -0.26]( 0.98) I don't see any regression / improvements from a performance standpoint on my 3rd Generation EPYC system (2 x 64C/128T. boost on, C2 disabled) Feel free to include: Tested-by: K Prateek Nayak > > Oleg. > -- Thanks and Regards, Prateek