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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by CY4PEPF0000FCC0.mail.protection.outlook.com (10.167.242.102) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9564.3 via Frontend Transport; Fri, 23 Jan 2026 16:39:11 +0000 Received: from satlexmb08.amd.com (10.181.42.217) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Fri, 23 Jan 2026 10:39:10 -0600 Received: from [172.31.184.125] (10.180.168.240) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Fri, 23 Jan 2026 10:39:06 -0600 Message-ID: <44c45e82-25e7-4d70-a46d-fb34e6aacbd6@amd.com> Date: Fri, 23 Jan 2026 22:09:05 +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] sched/eevdf: Update se->vprot in reweight_entity() To: Peter Zijlstra , Vincent Guittot CC: "wangtao (EQ)" , , , , , , , , , , References: <20260120123113.3518950-1-wangtao554@huawei.com> <8e7aadf8-b7a0-4500-ad2d-507665007694@amd.com> <15d8374f-b1a5-4946-829d-8e9c6ef39272@huawei.com> <20260123153854.GU166857@noisy.programming.kicks-ass.net> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20260123153854.GU166857@noisy.programming.kicks-ass.net> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Jan 2026 16:39:11.2296 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5973cd9b-de68-4912-6e7f-08de5a9defd3 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=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CY4PEPF0000FCC0.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB5625 Hello Peter, On 1/23/2026 9:08 PM, Peter Zijlstra wrote: > On Wed, Jan 21, 2026 at 06:00:15PM +0100, Vincent Guittot wrote: > >> Why not use update_protect_slice() like when a new task with a shorter >> slice is added ? > > That seems wrong too... > > I was going over this, and should we not limit set_protect_slice() to > the first set_next_entity(). That is, AFAICT we'll re-set it on > sched_change -- which sounds wrong to me. That makes sense. > > Anyway, I ended up with something like so (should probably be split in > two patches). > > --- > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index eca642295c4b..bab51da3d179 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3790,6 +3790,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, > unsigned long weight) > { > bool curr = cfs_rq->curr == se; > + u64 vprot = 0; > > if (se->on_rq) { > /* commit outstanding execution time */ > @@ -3797,6 +3798,9 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, > update_entity_lag(cfs_rq, se); > se->deadline -= se->vruntime; > se->rel_deadline = 1; > + if (curr && protect_slice(se)) > + vprot = se->vprot - se->vruntime; > + > cfs_rq->nr_queued--; > if (!curr) > __dequeue_entity(cfs_rq, se); > @@ -3812,6 +3816,9 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, > if (se->rel_deadline) > se->deadline = div_s64(se->deadline * se->load.weight, weight); > > + if (vprot) > + vprot = div_s64(vprot * se->load.weight, weight); > + > update_load_set(&se->load, weight); > > do { > @@ -3823,6 +3830,8 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, > enqueue_load_avg(cfs_rq, se); > if (se->on_rq) { > place_entity(cfs_rq, se, 0); > + if (vprot) > + se->vprot = se->vruntime + vprot; Scaling vprot makes sense too. Can there be a problem where "vprot" turns to zero on scaling (weight > (vprot * se->load.weight)) but we don't end up updating "se->vprot"? Probably rare but a higher weight implies it might take a tad bit longer to hit that old "vprot" but since we are losing the precision, can the pending "se->vprot" be big enough to cause any issue? Since we are looking at these bits, can you also please take a look at https://lore.kernel.org/lkml/20251226001731.3730586-1-quzicheng@huawei.com/ which I feel might be a genuine issue when we are reweight the curr's vruntime. > update_load_add(&cfs_rq->load, se->load.weight); > if (!curr) > __enqueue_entity(cfs_rq, se); -- Thanks and Regards, Prateek