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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: 82d22b41-450c-4a04-234c-08dae02ee4fa X-MS-Exchange-CrossTenant-originalarrivaltime: 17 Dec 2022 13:02:04.0593 (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: YTHKEsN/im4Y2yacwYyNvjOx5X4ULZMlObg2GV29QrVz5j86gqF3G751seCsSGs58yhFtWYNuqDEtmkY1UU/XA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR11MB6507 X-OriginatorOrg: intel.com X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 15, 2022 at 05:00:29PM +0800, Zqiang wrote: > Currently, when CPUs going offline, the rcu boost kthreads CPU > affinity has been reset in rcutree_offline_cpu(), therefore this > commit remove duplicate settings in rcutree_dead_cpu(). >=20 > Signed-off-by: Zqiang > >One question... > >Given that rcutree_offline_cpu() causes rcu_boost_kthread_setaffinity() >to be invoked with the number of the outgoing CPU, but rcutree_dead_cpu() >instead passes in -1, are these two invocations really redundant? > >Although -1 is passed in, but at this time, the outgoing CPU has been remo= ved from=20 >rcu_rnp_online_cpus(rnp), in other words, we will eliminate the same CPU,= which is >also we passed in cpu in the rcutree_offline_cpu() before. > I also used " qemu -smp 4 "for a simple test. 1) rcutree_offline_cpu() (gdb) bt #0 set_cpus_allowed_ptr (p=3Dp@entry=3D0xffff888100bd9cc0, new_mask=3Dnew_= mask@entry=3D0xffff888100ce7cd0) at kernel/sched/core.c:2939 #1 0xffffffff811be169 in rcu_boost_kthread_setaffinity (rnp=3D0xffffffff83= 7a4c00 , outgoingcpu=3Doutgoingcpu@entry=3D3) at kernel/rcu/tree_plugin.h:1250 #2 0xffffffff811cfa9f in rcutree_affinity_setting (outgoing=3D3, cpu=3D3) = at kernel/rcu/tree.c:4297 #3 rcutree_offline_cpu (cpu=3D3) at kernel/rcu/tree.c:4341 #4 0xffffffff810c4e6f in cpuhp_invoke_callback (cpu=3Dcpu@entry=3D3, state= =3Dstate@entry=3DCPUHP_AP_RCUTREE_ONLINE, bringup=3Dbringup@entry=3Dfalse, node=3D, lastp=3Dlastp@= entry=3D0xffff88815b027568) at kernel/cpu.c:192 #5 0xffffffff810c6e24 in cpuhp_thread_fun (cpu=3D) at kerne= l/cpu.c:785 #6 0xffffffff8111784e in smpboot_thread_fn (data=3D0xffff88810014c3c0) at = kernel/smpboot.c:164 #7 0xffffffff8110c88e in kthread (_create=3D0xffff8881009b8b00) at kernel/= kthread.c:376 #8 0xffffffff81002902 in ret_from_fork () at arch/x86/entry/entry_64.S:306 #9 0x0000000000000000 in ?? () (gdb) p/x *0xffff888100ce7cd0 $1 =3D 0x7 2) rcutree_dead_cpu() #0 set_cpus_allowed_ptr (p=3Dp@entry=3D0xffff888100bd9cc0, new_mask=3Dnew_= mask@entry=3D0xffff888109fc7948) at kernel/sched/core.c:2939 #1 0xffffffff811be169 in rcu_boost_kthread_setaffinity (rnp=3D0xffffffff83= 7a4c00 , outgoingcpu=3Doutgoingcpu@entry=3D-1) at kernel/rcu/tree_plugin.h:1250 #2 0xffffffff811cf4a1 in rcutree_dead_cpu (cpu=3D3) at kernel/rcu/tree.c:4= 176 #3 0xffffffff810c4e6f in cpuhp_invoke_callback (cpu=3Dcpu@entry=3D3, state= =3DCPUHP_RCUTREE_PREP, bringup=3Dbringup@entry=3Dfalse, node=3Dnode@entry=3D0x0 , lastp=3Dlastp@entry=3D0x0 = ) at kernel/cpu.c:192 #4 0xffffffff810c58f5 in cpuhp_invoke_callback_range (bringup=3Dbringup@en= try=3Dfalse, cpu=3Dcpu@entry=3D3, st=3Dst@entry=3D0xffff88815b027540, target=3Dtarget@entry=3DCPUHP_OFFLI= NE) at kernel/cpu.c:675 #5 0xffffffff827a5f6a in cpuhp_down_callbacks (target=3DCPUHP_OFFLINE, st= =3D0xffff88815b027540, cpu=3D3) at kernel/cpu.c:1170 #6 _cpu_down (cpu=3Dcpu@entry=3D3, tasks_frozen=3Dtasks_frozen@entry=3D0, = target=3Dtarget@entry=3DCPUHP_OFFLINE) at kernel/cpu.c:1170 #7 0xffffffff810c6ff8 in cpu_down_maps_locked (target=3DCPUHP_OFFLINE, cpu= =3D3) at kernel/cpu.c:1202 #8 cpu_down (cpu=3D3, target=3Dtarget@entry=3DCPUHP_OFFLINE) at kernel/cpu= .c:1210 #9 0xffffffff810c7906 in cpu_device_down (dev=3Ddev@entry=3D0xffff88815b02= 6988) at kernel/cpu.c:1227 (gdb) p/x *0xffff888109fc7948 $2 =3D 0x7 As can be seen from the above, we have set the same cpumask twice for the s= ame boost kthreads. Thanks Zqiang >Thanks >Zqiang > > Thanx, paul > --- > kernel/rcu/tree.c | 5 ----- > 1 file changed, 5 deletions(-) >=20 > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 65f3dd2fd3ae..20de83ed0c7e 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -4122,15 +4122,10 @@ static void rcu_cleanup_dead_rnp(struct rcu_node = *rnp_leaf) > */ > int rcutree_dead_cpu(unsigned int cpu) > { > - struct rcu_data *rdp =3D per_cpu_ptr(&rcu_data, cpu); > - struct rcu_node *rnp =3D rdp->mynode; /* Outgoing CPU's rdp & rnp. */ > - > if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) > return 0; > =20 > WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); > - /* Adjust any no-longer-needed kthreads. */ > - rcu_boost_kthread_setaffinity(rnp, -1); > // Stop-machine done, so allow nohz_full to disable tick. > tick_dep_clear(TICK_DEP_BIT_RCU); > return 0; > --=20 > 2.25.1 >=20