linux-kernel - Re: [rt-patch 4/3] arm,KVM: Move phys_timer handling to hard irq context

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Date:   Sat, 04 Aug 2018 14:25:20 +0200
From:   Mike Galbraith <efault@....de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [rt-patch 4/3] arm,KVM: Move phys_timer handling to hard irq
 context

On Thu, 2018-08-02 at 19:43 +0200, Mike Galbraith wrote:
> On Thu, 2018-08-02 at 18:50 +0200, Mike Galbraith wrote:
> > On Thu, 2018-08-02 at 12:31 -0400, Steven Rostedt wrote:
> > > On Thu, 02 Aug 2018 08:56:20 +0200
> > > Mike Galbraith <efault@....de> wrote:
> > > 
> > > > (arm-land adventures 1/3 take2 will have to wait, my cup runeth over) 
> > > > 
> > > > v4.14..v4.15 timer handling changes including calling kvm_timer_vcpu_load()
> > > 
> > > I take it that this should be added to v4.16-rt and marked stable-rt?
> > 
> > Yeah, barring way sexier ideas of course.
> 
> Gah, wait.  WRT marking for stable-rt, only the pmu allocation splat
> fix is applicable to @stable-rt, kvm locking woes start at 4.15.

None of that series got picked up, so the pmu patch is moot as well. 
The warning is harmless anyway.

Besides, there are more interesting fish in the arm64 sea than kvm.

virgin 4.16.18-rt12-rt

[  537.236131] ITS queue timeout (65440 65504 4640)
[  537.236150] ITS cmd its_build_inv_cmd failed
[  537.236160] sched: RT throttling activated
[ 1229.180124] ITS queue timeout (65440 65504 3744)
[ 1229.180134] ITS cmd its_build_inv_cmd failed

(converts those to trace_printk [invalidating virgin source warantee])

# tracer: nop
#
#                              _-----=> irqs-off
#                             / _----=> need-resched
#                            | /  _----=> need-resched_lazy
#                            || / _---=> hardirq/softirq
#                            ||| / _--=> preempt-depth
#                            |||| /     delay
#           TASK-PID   CPU#  |||||    TIMESTAMP  FUNCTION
#              | |       |   |||||       |         |
          <idle>-0     [000] d..h2..    84.967153: its_wait_for_range_completion+0xa8/0xe0: ITS queue timeout (65440 65504 96)
          <idle>-0     [000] d..h2..    84.967155: its_send_single_command+0xd4/0x130: ITS cmd its_build_inv_cmd failed

(starts cyclictest+kbuild)

[ 9609.602489] NOHZ: local_softirq_pending 10
[10089.311713] NOHZ: local_softirq_pending 80
[10089.311735] NOHZ: local_softirq_pending 80
[10097.315809] NOHZ: local_softirq_pending 80
[10112.262436] NOHZ: local_softirq_pending 10
[10118.966066] NOHZ: local_softirq_pending 80
[10121.211106] NOHZ: local_softirq_pending 80
[10121.287093] NOHZ: local_softirq_pending 80
[10329.501202] NOHZ: local_softirq_pending 80
[10329.501231] NOHZ: local_softirq_pending 80

T:60 (17291) P:99 I:31000 C:  18128 Min:      5 Act:   12 Avg:  107 Max: 1581163 <== Thar she blows!

 irq/464-eth0-Tx-3955  [060] d...111 11015.059743: its_wait_for_range_completion+0xa8/0xe0: ITS queue timeout (65440 65504 5280)
 irq/464-eth0-Tx-3955  [060] d...111 11015.059749: <stack trace>
 => irq_chip_unmask_parent+0x2c/0x38
 => its_unmask_msi_irq+0x28/0x38
 => unmask_irq.part.4+0x30/0x50
 => unmask_threaded_irq+0x4c/0x58
 => irq_finalize_oneshot.part.2+0x9c/0x100
 => irq_forced_thread_fn+0x60/0x98
 => irq_thread+0x148/0x1e0
 => kthread+0x140/0x148
 => ret_from_fork+0x10/0x18
 irq/464-eth0-Tx-3955  [060] d...111 11015.059751: its_send_single_command+0xd4/0x130: ITS cmd its_build_inv_cmd failed
 irq/464-eth0-Tx-3955  [060] d...111 11015.059752: <stack trace>
 => its_unmask_msi_irq+0x28/0x38
 => unmask_irq.part.4+0x30/0x50
 => unmask_threaded_irq+0x4c/0x58
 => irq_finalize_oneshot.part.2+0x9c/0x100
 => irq_forced_thread_fn+0x60/0x98
 => irq_thread+0x148/0x1e0
 => kthread+0x140/0x148
 => ret_from_fork+0x10/0x18
 irq/464-eth0-Tx-3955  [060] d..h311 11015.059764: update_curr_rt+0x280/0x320: sched: RT throttling activated
 irq/464-eth0-Tx-3955  [060] d..h311 11015.059765: <stack trace>
 => update_process_times+0x48/0x60
 => tick_sched_handle.isra.5+0x34/0x70
 => tick_sched_timer+0x54/0xa8
 => __hrtimer_run_queues+0xf8/0x388
 => hrtimer_interrupt+0xe4/0x258
 => arch_timer_handler_phys+0x38/0x58
 => handle_percpu_devid_irq+0xa8/0x2c8
 => generic_handle_irq+0x34/0x50
 => __handle_domain_irq+0x8c/0x100
 => gic_handle_irq+0x80/0x18c
 => el1_irq+0xb4/0x13c
 => _raw_spin_unlock_irq+0x2c/0x78
 => irq_finalize_oneshot.part.2+0x6c/0x100
 => irq_forced_thread_fn+0x60/0x98
 => irq_thread+0x148/0x1e0
 => kthread+0x140/0x148
 => ret_from_fork+0x10/0x18
          <idle>-0     [008] d..h3.. 11015.374565: sched_rt_period_timer+0x2f0/0x420: sched: RT throttling deactivated
          <idle>-0     [008] d..h3.. 11015.374570: <stack trace>
 => arch_timer_handler_phys+0x38/0x58
 => handle_percpu_devid_irq+0xa8/0x2c8
 => generic_handle_irq+0x34/0x50
 => __handle_domain_irq+0x8c/0x100
 => gic_handle_irq+0x80/0x18c
 => el1_irq+0xb4/0x13c
 => arch_cpu_idle+0x2c/0x1d0
 => default_idle_call+0x30/0x48
 => do_idle+0x1c4/0x218
 => cpu_startup_entry+0x2c/0x30
 => secondary_start_kernel+0x184/0x1d0