linux-kernel - Re: [patch 1/2] tick/broadcast: Prevent deep idle states if no broadcast device available

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Date:	Mon, 06 Jul 2015 17:27:31 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Sudeep Holla <sudeep.holla@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Suzuki Poulose <Suzuki.Poulose@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [patch 1/2] tick/broadcast: Prevent deep idle states if no broadcast
 device available



On 06/07/15 17:06, Thomas Gleixner wrote:
> On Mon, 6 Jul 2015, Sudeep Holla wrote:
>> On 06/07/15 16:35, Thomas Gleixner wrote:
>>> Well, we should figure out what happens while we are at it before
>>> everything gets paged out again.
>>>
>>
>> True. I just wanted to mention that this patch works for all the
>> practical purposes.
>>
>>> In the case of CONFIG_NOHZ=n and CONFIG_HIGHRES=n the broadcast
>>> hrtimer is not compiled as it depends on CONFIG_TICK_ONESHOT, so it
>>> works via the bc.evtdev == NULL check.
>>>
>>> With either option enabled CONFIG_TICK_ONESHOT gets set, so the
>>> broadcast timer gets installed but somehow does not work proper if
>>> nohz and highres are disabled on the kernel command line.
>>>
>>
>> Let me know if you want to test something to help debug this configuration.
>
> Can you try the following delta patch?
>

I just tried the failing configuration. Yes I am able to boot now, 
however made below 2 observations:

1. As in the case of CONFIG_HZ_PERIODIC, none of the CPUs enters deeper
    idle states losing local timers. So the behaviour is same in both
    versions of periodic mode of timer operation.
2. After boot I am seeing the below warning:

------------[ cut here ]------------
WARNING: CPU: 1 PID: 0 at kernel/time/hrtimer.c:1247 
__hrtimer_run_queues+0x148/0x150()
Modules linked in:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.2.0-rc1 #573
Hardware name: ARM Juno development board (r0) (DT)
Call trace:
[<ffffffc000089954>] dump_backtrace+0x0/0x124
[<ffffffc000089a88>] show_stack+0x10/0x1c
[<ffffffc0005d100c>] dump_stack+0x84/0xc8
[<ffffffc0000b3f34>] warn_slowpath_common+0x98/0xd0
[<ffffffc0000b402c>] warn_slowpath_null+0x14/0x20
[<ffffffc000101eec>] __hrtimer_run_queues+0x144/0x150
[<ffffffc0001028b4>] hrtimer_run_queues+0xb8/0xe8
[<ffffffc000101714>] update_process_times+0x28/0x6c
[<ffffffc00010d978>] tick_periodic+0x3c/0xb8
[<ffffffc00010da1c>] tick_handle_periodic+0x28/0x94
[<ffffffc0004d6154>] arch_timer_handler_phys+0x28/0x38
[<ffffffc0000f5964>] handle_percpu_devid_irq+0x74/0x9c
[<ffffffc0000f1668>] generic_handle_irq+0x30/0x4c
[<ffffffc0000f1984>] __handle_domain_irq+0x5c/0xac
[<ffffffc0000824a8>] gic_handle_irq+0x30/0x80
Exception stack(0xffffffc9768ffdb0 to 0xffffffc9768ffed0)
fda0:                                     8c1625f8 00000008 75da4800 
ffffffc9
fdc0: 768ffef0 ffffffc9 004b3448 ffffffc0 00000000 00000000 768fc000 
ffffffc9
fde0: 00000000 00000000 00000001 00000000 00000002 00000000 00000000 
00000000
fe00: da98d76d 001e70a3 000005dc 00000000 00000003 00000000 00000001 
00000000
fe20: 00000004 00000000 00000040 00000000 ffffffff ffffffff 00000000 
00000000
fe40: 008a3dd8 ffffffc0 ffffffff ffffffff 001a65a0 ffffffc0 004e2488 
00000000
fe60: f7ea3080 0000007f 8c1625f8 00000008 75da4800 ffffffc9 00000000 
00000000
fe80: 008da840 ffffffc0 8b7dc4e5 00000008 768fff70 ffffffc9 00884e20 
ffffffc0
fea0: 005e8770 ffffffc0 00896000 ffffffc0 768fc000 ffffffc9 768ffef0 
ffffffc9
fec0: 004b3408 ffffffc0 768ffef0 ffffffc9
[<ffffffc0000855a4>] el1_irq+0x64/0xd8
[<ffffffc0004b354c>] cpuidle_enter+0x14/0x20
[<ffffffc0000e80f8>] call_cpuidle+0x24/0x50
[<ffffffc0000e8268>] cpu_startup_entry+0x144/0x224
[<ffffffc00009010c>] secondary_start_kernel+0x124/0x14c
---[ end trace 87fd96b94f030e33 ]---
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