Message-ID: <5b39aebc3f17982c2e374d3f7e0320f429055dd0.camel@linux.intel.com>
Date:   Mon, 10 Feb 2020 07:16:51 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>, bberg@...hat.com,
        bp@...en8.de, hpa@...or.com, mingo@...hat.com, tglx@...utronix.de,
        tony.luck@...el.com
Cc:     x86@...nel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, hdegoede@...hat.com,
        ckellner@...hat.com
Subject: Re: [PATCH] x86, mce, therm_throt: Optimize notifications of
 thermal throttle

On Sat, 2020-02-08 at 22:09 -0800, Srinivas Pandruvada wrote:
> On Sat, 2020-02-08 at 22:24 +0000, Chris Wilson wrote:
> > Quoting Srinivas Pandruvada (2019-11-11 21:43:12)
> > > +static void throttle_active_work(struct work_struct *work)
> > > +{
> > > +       struct _thermal_state *state =
> > > container_of(to_delayed_work(work),
> > > +                                               struct
> > > _thermal_state, therm_work);
> > > +       unsigned int i, avg, this_cpu = smp_processor_id();
> > > +       u64 now = get_jiffies_64();
> > > +       bool hot;
> > > +       u8 temp;
> > 
> > <6> [198.901895] [IGT] perf_pmu: starting subtest cpu-hotplug
> > <4> [199.088851] IRQ 24: no longer affine to CPU0
> > <4> [199.088871] IRQ 25: no longer affine to CPU0
> > <6> [199.091679] smpboot: CPU 0 is now offline
> > <6> [200.122204] smpboot: Booting Node 0 Processor 0 APIC 0x0
> > <6> [200.297267] smpboot: CPU 1 is now offline
> > <3> [201.218812] BUG: using smp_processor_id() in preemptible
> > [00000000] code: kworker/1:0/17
> > <4> [201.218974] caller is throttle_active_work+0x12/0x280
> > <4> [201.218985] CPU: 0 PID: 17 Comm: kworker/1:0 Tainted:
> > G     U            5.5.0-CI-CI_DRM_7867+ #1
> > <4> [201.218991] Hardware name: MSI MS-7924/Z97M-G43(MS-7924), BIOS
> > V1.12 02/15/2016
> > <4> [201.219001] Workqueue: events throttle_active_work
> > <4> [201.219009] Call Trace:
> > <4> [201.219021]  dump_stack+0x71/0x9b
> > <4> [201.219035]  debug_smp_processor_id+0xad/0xb0
> > <4> [201.219047]  throttle_active_work+0x12/0x280
> > <4> [201.219063]  process_one_work+0x26a/0x620
> > <4> [201.219087]  worker_thread+0x37/0x380
> > <4> [201.219103]  ? process_one_work+0x620/0x620
> > <4> [201.219110]  kthread+0x119/0x130
> > <4> [201.219119]  ? kthread_park+0x80/0x80
> > <4> [201.219134]  ret_from_fork+0x3a/0x50
> > <6> [201.315866] x86: Booting SMP configuration:
> > <6> [201.315880] smpboot: Booting Node 0 Processor 1 APIC 0x2
> > <4> [201.319814] ------------[ cut here ]------------
> > <3> [201.319832] ODEBUG: init active (active state 0) object type:
> > timer_list hint: delayed_work_timer_fn+0x0/0x10
> > <4> [201.319971] WARNING: CPU: 1 PID: 14 at lib/debugobjects.c:484
> > debug_print_object+0x67/0x90
> > <4> [201.319977] Modules linked in: vgem snd_hda_codec_hdmi i915
> > mei_hdcp x86_pkg_temp_thermal coretemp snd_hda_codec_realtek
> > crct10dif_pclmul snd_hda_codec_generic crc32_pclmul snd_hda_intel
> > snd_intel_dspcfg snd_hda_codec ghash_clmulni_intel snd_hwdep
> > snd_hda_core snd_pcm mei_me r8169 mei realtek lpc_ich prime_numbers
> > <4> [201.320023] CPU: 1 PID: 14 Comm: cpuhp/1 Tainted:
> > G     U            5.5.0-CI-CI_DRM_7867+ #1
> > <4> [201.320029] Hardware name: MSI MS-7924/Z97M-G43(MS-7924), BIOS
> > V1.12 02/15/2016
> > <4> [201.320038] RIP: 0010:debug_print_object+0x67/0x90
> > <4> [201.320046] Code: 83 c2 01 8b 4b 14 4c 8b 45 00 89 15 17 f7 8b
> > 02 8b 53 10 4c 89 e6 48 c7 c7 b0 ce 31 82 48 8b 14 d5 00 37 07 82
> > e8
> > 89 7b b8 ff <0f> 0b 5b 83 05 33 fb 21 01 01 5d 41 5c c3 83 05 28 fb
> > 21 01 01 c3
> > <4> [201.320053] RSP: 0000:ffffc900000dbd40 EFLAGS: 00010286
> > <4> [201.320060] RAX: 0000000000000000 RBX: ffff888408665d68 RCX:
> > 0000000000000001
> > <4> [201.320066] RDX: 0000000080000001 RSI: ffff88840d6e30f8 RDI:
> > 00000000ffffffff
> > <4> [201.320072] RBP: ffffffff826489e0 R08: ffff88840d6e30f8 R09:
> > 0000000000000000
> > <4> [201.320078] R10: 0000000000000000 R11: 0000000000000000 R12:
> > ffffffff822d7bd1
> > <4> [201.320084] R13: ffffffff826489e0 R14: ffff88840f898300 R15:
> > 0000000000000202
> > <4> [201.320091] FS:  0000000000000000(0000)
> > GS:ffff88840f880000(0000) knlGS:0000000000000000
> > <4> [201.320098] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > <4> [201.320104] CR2: 0000000000000000 CR3: 0000000005610001 CR4:
> > 00000000001606e0
> > <4> [201.320109] Call Trace:
> > <4> [201.320125]  __debug_object_init+0x359/0x510
> > <4> [201.320140]  ? _raw_spin_unlock_irqrestore+0x34/0x60
> > <4> [201.320156]  ? queue_work_node+0x70/0x70
> > <4> [201.320165]  init_timer_key+0x25/0x140
> > <4> [201.320180]  ? intel_thermal_supported+0x30/0x30
> > <4> [201.320191]  thermal_throttle_online+0xb4/0x260
> > <4> [201.320204]  ? unexpected_thermal_interrupt+0x20/0x20
> > <4> [201.320213]  cpuhp_invoke_callback+0x9b/0x9d0
> > <4> [201.320235]  cpuhp_thread_fun+0x1c8/0x220
> > <4> [201.320249]  ? smpboot_thread_fn+0x23/0x280
> > <4> [201.320259]  ? smpboot_thread_fn+0x6b/0x280
> > <4> [201.320271]  smpboot_thread_fn+0x1d3/0x280
> > <4> [201.320288]  ? sort_range+0x20/0x20
> > <4> [201.320295]  kthread+0x119/0x130
> > <4> [201.320303]  ? kthread_park+0x80/0x80
> > <4> [201.320317]  ret_from_fork+0x3a/0x50
> > <4> [201.320348] irq event stamp: 4846
> > <4> [201.320358] hardirqs last  enabled at (4845):
> > [<ffffffff8112dcca>] console_unlock+0x4ba/0x5a0
> > <4> [201.320368] hardirqs last disabled at (4846):
> > [<ffffffff81001ca0>] trace_hardirqs_off_thunk+0x1a/0x1c
> > <4> [201.320379] softirqs last  enabled at (4746):
> > [<ffffffff81e00385>] __do_softirq+0x385/0x47f
> > <4> [201.320388] softirqs last disabled at (4739):
> > [<ffffffff810ba15a>] irq_exit+0xba/0xc0
> > <4> [201.320394] ---[ end trace 06576bf31ad2ac2b ]---
> > 
> > Are we otherwise relying on current->nr_cpus_allowed == 1 here?
> No.
> I am checking internally, if I can use raw_smp_processor_id()
> instead.
Let me correct my answer.
Here the call is from a workqueue callback which is scheduled to
execute on a specific CPU using schedule_delayed_work_on().
Meanwhile if the CPU is offline or dead, not sure if the thread can
execute on another CPU.

Thanks,
Srinivas




> 
> Thanks,
> Srinivas
> 
> > (As this section is not within a preempt_disable or
> > local_irq_disable
> > region.)
> > -Chris

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