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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: PH0PR11MB5880.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: d0e81acf-3055-4fef-abc9-08d9cf5d977a X-MS-Exchange-CrossTenant-originalarrivaltime: 04 Jan 2022 08:38:32.9006 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: Sj8fp7TBAOvd8RAq2U0ZQvhlvJGrMUXkj/dDf8lH3Cld1FruhLfriJ+fxNC0y/eFRu06eeGj2H9z+Th7uZ4BPw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR11MB5942 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 03, 2022 at 02:17:11PM +0100, Sebastian Andrzej Siewior wrote: > On 2022-01-01 08:44:26 [-0800], Paul E. McKenney wrote: > > On Wed, Dec 29, 2021 at 12:05:10AM +0800, Zqiang wrote: > > > In non-RT kernel, if the RCU_BOOST is enabled, the per-cpu rcuc=20 > > > kthread will be created, however under the rcutree.use_softirq=3D1,=20 > > > the RCU core processing only in softirq context, the rcuc kthread=20 > > > doesn't do anything, so remove RCU_BOOST interference. > > >=20 > > > Signed-off-by: Zqiang > >=20 > > Looks sane to me, but adding Sebastian on CC for his thoughts. >=20 > Yes, it makes sense. invoke_rcu_core_kthread() is only invoked for=20 > !use_softirq so it makes to create the threads based on this condition. >=20 > Acked-by: Sebastian Andrzej Siewior Thanks Sebastian review. >Thank you both! As usual, I could not resist a bit of wordsmithing, pleas= e see below. Hi Paul , thank you for your modification, your description is clearer. Thanks, Zqiang > > Thanx, Paul > >------------------------------------------------------------------------ > >commit 6e68b781388cfaca95a07493a060c4a6e4ee5d0f >Author: Zqiang >Date: Wed Dec 29 00:05:10 2021 +0800 > > rcu: Create per-cpu rcuc kthreads only when rcutree.use_softirq=3D0 > =20 > The per-CPU "rcuc" kthreads are used only by kernels booted with > rcutree.use_softirq=3D0, but they are nevertheless unconditionally cre= ated > by kernels built with CONFIG_RCU_BOOST=3Dy. This results in "rcuc" > kthreads being created that are never actually used. This commit > therefore refrains from creating these kthreads unless the kernel > is actually booted with rcutree.use_softirq=3D0. =20 > Acked-by: Sebastian Andrzej Siewior > Signed-off-by: Zqiang > Signed-off-by: Paul E. McKenney > >diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index aeea5487632f7..5c= 0ffee7a43a0 100644 >--- a/kernel/rcu/tree.c >+++ b/kernel/rcu/tree.c >@@ -2903,7 +2903,7 @@ static int __init rcu_spawn_core_kthreads(void) >=20 > for_each_possible_cpu(cpu) > per_cpu(rcu_data.rcu_cpu_has_work, cpu) =3D 0; >- if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq) >+ if (use_softirq) > return 0; > WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), > "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __= func__);