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Thu, 25 May 2023 03:07:58 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ6qM4l0aFUNyAaglZIDdVq94GoCTUm/JXTXxeRLQlYpY5fMAkmavlsUCvohYLfu27wF+uBPMA== X-Received: by 2002:a1c:4c11:0:b0:3f4:2cb2:a6cf with SMTP id z17-20020a1c4c11000000b003f42cb2a6cfmr2191016wmf.10.1685009278201; Thu, 25 May 2023 03:07:58 -0700 (PDT) Received: from vschneid.remote.csb ([154.57.232.159]) by smtp.gmail.com with ESMTPSA id o7-20020a05600c378700b003f4ddde398csm1582641wmr.21.2023.05.25.03.07.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 May 2023 03:07:57 -0700 (PDT) From: Valentin Schneider To: Yicong Yang , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org Cc: rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, yu.c.chen@intel.com, linuxarm@huawei.com, prime.zeng@huawei.com, wangjie125@huawei.com, yangyicong@hisilicon.com Subject: Re: [PATCH] sched/fair: Don't balance task to its current running CPU In-Reply-To: <20230524072018.62204-1-yangyicong@huawei.com> References: <20230524072018.62204-1-yangyicong@huawei.com> Date: Thu, 25 May 2023 11:07:55 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24/05/23 15:20, Yicong Yang wrote: > From: Yicong Yang > > We've run into the case that the balancer tries to balance a migration > disabled task and trigger the warning in set_task_cpu() like below: > > ------------[ cut here ]------------ > WARNING: CPU: 7 PID: 0 at kernel/sched/core.c:3115 set_task_cpu+0x188/0x240 > Modules linked in: hclgevf xt_CHECKSUM ipt_REJECT nf_reject_ipv4 <...snip> > CPU: 7 PID: 0 Comm: swapper/7 Kdump: loaded Tainted: G O 6.1.0-rc4+ #1 > Hardware name: Huawei TaiShan 2280 V2/BC82AMDC, BIOS 2280-V2 CS V5.B221.01 12/09/2021 > pstate: 604000c9 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > pc : set_task_cpu+0x188/0x240 > lr : load_balance+0x5d0/0xc60 > sp : ffff80000803bc70 > x29: ffff80000803bc70 x28: ffff004089e190e8 x27: ffff004089e19040 > x26: ffff007effcabc38 x25: 0000000000000000 x24: 0000000000000001 > x23: ffff80000803be84 x22: 000000000000000c x21: ffffb093e79e2a78 > x20: 000000000000000c x19: ffff004089e19040 x18: 0000000000000000 > x17: 0000000000001fad x16: 0000000000000030 x15: 0000000000000000 > x14: 0000000000000003 x13: 0000000000000000 x12: 0000000000000000 > x11: 0000000000000001 x10: 0000000000000400 x9 : ffffb093e4cee530 > x8 : 00000000fffffffe x7 : 0000000000ce168a x6 : 000000000000013e > x5 : 00000000ffffffe1 x4 : 0000000000000001 x3 : 0000000000000b2a > x2 : 0000000000000b2a x1 : ffffb093e6d6c510 x0 : 0000000000000001 > Call trace: > set_task_cpu+0x188/0x240 > load_balance+0x5d0/0xc60 > rebalance_domains+0x26c/0x380 > _nohz_idle_balance.isra.0+0x1e0/0x370 > run_rebalance_domains+0x6c/0x80 > __do_softirq+0x128/0x3d8 > ____do_softirq+0x18/0x24 > call_on_irq_stack+0x2c/0x38 > do_softirq_own_stack+0x24/0x3c > __irq_exit_rcu+0xcc/0xf4 > irq_exit_rcu+0x18/0x24 > el1_interrupt+0x4c/0xe4 > el1h_64_irq_handler+0x18/0x2c > el1h_64_irq+0x74/0x78 > arch_cpu_idle+0x18/0x4c > default_idle_call+0x58/0x194 > do_idle+0x244/0x2b0 > cpu_startup_entry+0x30/0x3c > secondary_start_kernel+0x14c/0x190 > __secondary_switched+0xb0/0xb4 > ---[ end trace 0000000000000000 ]--- > > Further investigation shows that the warning is superfluous, the migration > disabled task is just going to be migrated to its current running CPU. > This is because that on load balance if the dst_cpu is not allowed by the > task, we'll re-select a new_dst_cpu as a candidate. If no task can be > balanced to dst_cpu we'll try to balance the task to the new_dst_cpu > instead. In this case when the migration disabled task is not on CPU it > only allows to run on its current CPU, load balance will select its > current CPU as new_dst_cpu and later triggers the the warning above. > > This patch tries to solve this by not select the task's current running > CPU as new_dst_cpu in the load balance. > > Signed-off-by: Yicong Yang Thanks! Reviewed-by: Valentin Schneider