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client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by CH2PEPF00000147.mail.protection.outlook.com (10.167.244.104) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.113.7 via Frontend Transport; Fri, 12 Jun 2026 06:07:52 +0000 Received: from Satlexmb09.amd.com (10.181.42.218) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.41; Fri, 12 Jun 2026 01:07:51 -0500 Received: from satlexmb08.amd.com (10.181.42.217) by satlexmb09.amd.com (10.181.42.218) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.41; Thu, 11 Jun 2026 23:07:51 -0700 Received: from [10.136.37.196] (10.180.168.240) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server id 15.2.2562.41 via Frontend Transport; Fri, 12 Jun 2026 01:07:47 -0500 Message-ID: <380d53e2-3671-4327-a613-cf35c58b55d9@amd.com> Date: Fri, 12 Jun 2026 11:37:46 +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 v3 02/10] sched/fair: Credit a persistent, queue-depth-scaled vlag margin To: Wanpeng Li , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "Paolo Bonzini" , Sean Christopherson CC: Christian Borntraeger , Steven Rostedt , Vincent Guittot , "Juri Lelli" , , , Wanpeng Li , Richie Buturla References: <20260612013355.59231-1-kernellwp@gmail.com> <20260612013355.59231-3-kernellwp@gmail.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20260612013355.59231-3-kernellwp@gmail.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: Ht8ZfMTdQVuzqEsbeo9Og2LQ4Shtc2tOFAJD44qpQZoipj5B84vY21G2KOjzLpSJtW+oCu/YqJM+gqTKOWc8ELQ65O2uofWMqHG4YYPthIOrSmVlMiR1OnSPE/0rU4lE5/sI8cTlOOR+UiblubeBOWI7IRzVUUNl+oY326T1jSOsMD8iIJ9TW4Bg5MSi3pI6RQFtwetFII6XvIhVonI+m6UJuMFANVdci17utqlEXv25OWDLoYj3RiMNnFt0p6lEFf5mcldt+bO3aohNCFkVpqsXKxiqzUdT4yUdwQcbRnKg/leuMo+KoArCW5I9gnauITvXuUtg1dpofBcHrHHUoOkqmdqctAxPIWcyu/9r/5avE+i3DDPVzAV8JSaHNwkCkhDQO7PxuykP+DbixgsO1L+KJSGb0BzId7Bd8C8rRRQKZUO87J5mr2Z79eP99U0Z X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jun 2026 06:07:52.0374 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 83ba4123-422f-4c56-806b-08dec848efe1 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=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH2PEPF00000147.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA3PR12MB7975 Hello Wanpeng, On 6/12/2026 7:03 AM, Wanpeng Li wrote: > - /* Already eligible: nothing to do. */ > - if (vlag >= 0) > - return; > + /* Clamp the margin to entity_lag()'s bound so place_entity() keeps it. */ > + max_slice = cfs_rq_max_slice(cfs_rq) + TICK_NSEC; > + lag_limit = calc_delta_fair(max_slice, se); > + margin = eevdf_persistent_margin(cfs_rq, se); > + if (lag_limit && margin > lag_limit) > + margin = lag_limit; > + if (vlag >= 0) { > + if ((u64)vlag >= margin) > + return; > + want = margin - (u64)vlag; And we are making an eligible task more eligible but *where* is this credit coming from? Someone should be paying the price right? Just adding an arbitrary credit and then moving the task doing the yield_to() 0-lag point is simply not fair IMO. > + } else { > + want = margin + (u64)(-vlag); > + } -- Thanks and Regards, Prateek