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McKenney" , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] sched/fair: Disable DL server on rcu_torture_disable_rt_throttle() Message-ID: <20250316143955.GA2815370@joelnvbox> References: <20250306011014.2926917-1-joelagnelf@nvidia.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: IA1P220CA0006.NAMP220.PROD.OUTLOOK.COM (2603:10b6:208:461::11) To SN7PR12MB8059.namprd12.prod.outlook.com (2603:10b6:806:32b::7) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN7PR12MB8059:EE_|SA1PR12MB6869:EE_ X-MS-Office365-Filtering-Correlation-Id: afdda8d5-e131-4c30-5cd5-08dd64986c7e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?A458nzDVYbyd3qsCBNdQA7cmsu+Jz2gUk3p9CldduHJQlr+EPO8xRMOBMnpW?= =?us-ascii?Q?AbBlq5tioxvDDSufLq9qmUnlKwk1m/ajIV/GU860wlDEouxucyyjdiHhceYU?= =?us-ascii?Q?i95Zb9i/1OJuRA17Y3J0ZYoB2BqhyLl1gyty1T4ElTMi4ry7TEm4RTNpkwve?= =?us-ascii?Q?pP2NYpK/+RYsS2ai4RsktD2COCCf5aVJDQ9FMaw6f7Hti/jZekbe8Q5ef4l7?= =?us-ascii?Q?l28TM/TiD5Fh1B7XqXv30ycV/gjNQ9vHMzqufi/2/x0r7Q8QQSqYzi19fBeO?= =?us-ascii?Q?ZB6t2r5iBRdJcdKWnqfZMr9wxWq93oSWtkxVWvk7Qcj5Tz+7i78wo04bNCyF?= =?us-ascii?Q?DUbJaGGsKngvA/69siwpyUNtrxhsB+nX1Eh/2xP0bcNn0uFFITfHlxCg8MVe?= =?us-ascii?Q?KuJZm6yGFQXNLF08zyHcI+8ppbe4LIUB+zMr7Cq7rvXrJWvFJ3QqkMBvlKok?= =?us-ascii?Q?q4qyzyxdPyIx0l4qxEMKrCgCQ9mm6J6ljacJpXroeX7caP3WRUbUdWx+DARK?= =?us-ascii?Q?Z4UBVwADQhk5/bith/bl/l4Eb9yIO0Ea14QZWg5Lj2kQdLuXSwY9z6HToRFk?= =?us-ascii?Q?1vsM0YPuGNTv7qZ76GC507VUTze9aIOpfwsRjj+OgaD30LbGzujsfweb7R4+?= =?us-ascii?Q?avVjK97b+k6yIVeubEtQLdDLVRkP6NaXiVeU1EfW6mbyvaFXol8jGS6s+Tjc?= =?us-ascii?Q?YjLEZFhm3vCt4h9WhfFdxGPgYXo1x11fEO5Dx+loJL/8aWo0V5/Zz0vQCgq1?= =?us-ascii?Q?Dt14JpR/bswvW6N6Qqj2kUAJKbPwH5OqjLPcMFWoOd4RsziTPnKPLYfH0aO9?= =?us-ascii?Q?7uuULSP5avgpk0WP0qY7Irr12UK4er44UczumpnZuLscGtL1cJUxqx5njaeW?= =?us-ascii?Q?xaHHc9oouqUcoMd/J+RRygshCnu/DRgp994EOgWe/qCDdVniJRXKvuzhKqPk?= =?us-ascii?Q?o/7C0ARWunWio90LPNXLF9VUVRopnwP2/hTZ02jorBgEAwqw5a7XbiDbxtBq?= =?us-ascii?Q?eT4+lD7ISjS2hpm+0zQQzyGxAlFFqd0gJOzdSQK+Z3SPiHtb0NoWF6c0T+Vv?= =?us-ascii?Q?roYcGLgd6L7UpFKDO7oTa8TGg1d77uMlscFWJCDVMjpvmkaQjlYFbI1kbPuE?= =?us-ascii?Q?jQvhBax2I0x8L9aQollJ8pF3gBeR1zUCDZRLjzSgjBRKoRjZMqbKpTCWzfDW?= =?us-ascii?Q?cyioo9s7XT1TJo5IngtZ+1yHL+LSlMudtJA+jI7TvgTOJIF2wPfvxXZO1IIv?= =?us-ascii?Q?DKzreQtWZ/JJF7Su0lmfK5Y7Ho6oapEINCNllnB9axMWHcj6Gq6btygO+h0u?= =?us-ascii?Q?BDzMqHXmeT9osq0DU9Z4nMk5vYbwrMQSQiDaYSxP/6rKwcrEnXp3Usf2ws+6?= =?us-ascii?Q?hByUeCA68QOHshHEJ7JnqNMjKImu?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:SN7PR12MB8059.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(7416014)(376014)(366016);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?vj8/1sITvy++VarSVLd6saBap3CnAC+rUGkypNWama86Yvug9aJQvQc57ZSe?= =?us-ascii?Q?iNJr5B2CVV8jjP+9l6sUkVzMfHU0medw6s1aBCwCV1MXR4RCMpE6gTAIHjzV?= =?us-ascii?Q?5KrDunwkUDPZG0Gf959U2zdhTcvuzwXeVSA6lVBodeBvQZaf5dirJ2TP1xEr?= =?us-ascii?Q?F5u9GTUlFXIUzCSJhDAiYndFxhkdwumiubpt/dLQ7KaK8ukXDN67sB3jStwh?= =?us-ascii?Q?raYNePNTz99YCsKmqw+t9zywP8mYkxF2Ii2VsqkiWanTz3xMBaBbID4weGXF?= =?us-ascii?Q?ICKpDbfX/NN9xrl1hbiw7nFt9DsV4/dQVWDSgQ+FmOKYZ/o+Hr2+IcXSgMTn?= =?us-ascii?Q?Fef58vmvwgWHRavwRcyuC30Ad0F8yG6Ml3bIoxMrPpScbULWnMhcK8Odo76T?= =?us-ascii?Q?DX/lQcFYtfMvcxhZ5r8ZZabf8sLEWNTsB8vVC61O+MBDGAXOe/sqBnZowm5H?= =?us-ascii?Q?56mWBNaYqswfcg+HkK3AJTvuihqBWWf7VpRuLwHkGQmIH2KTKlQp9dx2VdjY?= =?us-ascii?Q?eift6P3KSgp9r8Xh6eR7XcNA6osy2eDf5x0KYPQoCAVGjJCYHNdtk1+b0RIU?= =?us-ascii?Q?z7CyuKos72WMCMAfO7DA9P7nDc9LapvTqGx4gLtQl7y+yzdp7hdDDgyowOTS?= =?us-ascii?Q?Erqs5b4cbpMueUdzyzCnztLM9PlruDgD4MS2RpA3QrpZGLZKNsmV4Ze4ahqx?= =?us-ascii?Q?0WFzTFWxzqePqYFUIXj907dKjIQ6Stxb7nLMEfIBBE2qyVv2Dvnh8aYYxCXI?= =?us-ascii?Q?xugGCDDeDeemFhGE6pnK+mEMlvVs5tgLngr0dpaJTjKOESWTMgnKWftgJqrl?= =?us-ascii?Q?BWo+AwKcZK0A1kmwGRkEE/45E7bqj4QeKDIpBNCT5igzqDN729Vbvj+wwubm?= =?us-ascii?Q?ODXr+V7UFytv/gBYfpB+ooNhz9HXtot0oWEKlUsYgoB//FR5u3UWbIxNcd9T?= =?us-ascii?Q?KWnKGWJlbJ3OEHh4V0CUxqRuxzTmu1bUxIBQdqPxHRobMtzQwmoc9ZPr83F8?= =?us-ascii?Q?mtQd0ZA3TpvvlFpNxO3rUzjFnF3sXCkG5DpqEOHElc/HHjTTCoj1MsGqs+In?= =?us-ascii?Q?06EFvaZ4f7I1/jtmZ5JjMDkd9ugzcTxO1I1NywLoOJhLlkIdabqagxkwcNQg?= =?us-ascii?Q?tZe7Ip/IW5Q0NPihamYSnQ3OOKQjjXoU+43w1QmGwPYZFryXd571qYsE28cD?= =?us-ascii?Q?tfTqDMYVL3DO6+redU5Z8ylRVjNrmYAQBeNwY7h0btq7UET6f7dWki7Pujqy?= =?us-ascii?Q?ru7iUUSMYtJSmuvmOrqb6jWnbGOeXqf7EkDGhdzR8VrY4shUfmAzoBHjaZQk?= =?us-ascii?Q?GJFS7l8U74ArZOSlTomFiuuWD4Pae1Xw4Y2WComa0S6gmZryqHfu6ad/Or8u?= =?us-ascii?Q?sjj6yz9lBot4mMeByqoHJsPyliOFw79A/NdcDM/nhPMBPKq93zJNsOrveat7?= =?us-ascii?Q?XniOVwxreDTBZGZg/KAXZzvJPPnhsBTUl55iMLH4Lz5/87SPC5yYszr8D2nv?= =?us-ascii?Q?pBGFMhEJo8m/GCGY3gOlSweGWa26JTPb1JFzK9FnfLY+/okHGw8gMJSvVjVk?= =?us-ascii?Q?v9K6S3qeIRS2CqrOtlF8KdJA+/uwseGkSUOk3zzQ?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: afdda8d5-e131-4c30-5cd5-08dd64986c7e X-MS-Exchange-CrossTenant-AuthSource: SN7PR12MB8059.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Mar 2025 14:39:57.5648 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: OZ6gRmKwwjPjFb6R/HH9Ef/TdAzdyfQEuHIF468o48YGRns6EdByqgWcYgPZ61Li/jjlanoEXoM8jCLuSWGXfQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB6869 On Thu, Mar 06, 2025 at 09:35:27AM +0000, Juri Lelli wrote: > Hi Joel, > > On 05/03/25 20:10, Joel Fernandes wrote: > > Currently, RCU boost testing in rcutorture is broken because it relies on > > having RT throttling disabled. This means the test will always pass (or > > rarely fail). This occurs because recently, RT throttling was replaced > > by DL server which boosts CFS tasks even when rcutorture tried to > > disable throttling (see rcu_torture_disable_rt_throttle()). However, the > > systctl_sched_rt_runtime variable is not considered thus still allowing > > RT tasks to be preempted by CFS tasks. > > > > Therefore this patch prevents DL server from starting when RCU torture > > sets the sysctl_sched_rt_runtime to -1. > > > > With this patch, boosting in TREE09 fails reliably if RCU_BOOST=n. > > > > Steven also mentioned that this could fix RT usecases where users do not > > want DL server to be interfering. > > > > Cc: stable@vger.kernel.org > > Cc: Paul E. McKenney > > Cc: Steven Rostedt > > Fixes: cea5a3472ac4 ("sched/fair: Cleanup fair_server") > > Signed-off-by: Joel Fernandes > > --- > > v1->v2: > > Updated Fixes tag (Steven) > > Moved the stoppage of DL server to fair (Juri) > > I think what I suggested/wondered (sorry if I wasn't clear) is that we > might need a link between sched_rt_runtime and the fair_server per-cpu > runtime under sched/debug (i.e., sched_fair_write(), etc), otherwise one > can end up with DL server disabled and still non zero runtime on the > debug interface. This is only if we want to make that link, though; > which I am not entirely sure it is something we want to do, as we will > be stuck with an old/legacy interface if we do. Peter? While we are discussing, would it be acceptable to provide a sysctl that disabled DL server? We could set this via boot parameters in rcutorture. That would unblock the testing. If feel that is OK to do considering another sysctl systctl_sched_rt_runtime is already there to disable RT throttling, so we are just adding a similar one for DL server. What do you think? thanks, - Joel