linux-kernel - Re: [PATCH v5 3/3] PM/runtime:Replace jiffies based accounting with ktime based accounting

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Message-ID: <43334acb-230c-c3e3-6b67-0813467c891f@roeck-us.net>
Date:   Mon, 21 Jan 2019 07:24:20 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        rodrigo.vivi@...el.com, David Airlie <airlied@...ux.ie>,
        Intel graphics driver community testing & development 
        <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v5 3/3] PM/runtime:Replace jiffies based accounting with
 ktime based accounting

On 1/21/19 7:17 AM, Vincent Guittot wrote:
> On Fri, 18 Jan 2019 at 13:08, Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On 1/18/19 3:05 AM, Rafael J. Wysocki wrote:
>>> On Fri, Jan 18, 2019 at 11:53 AM Vincent Guittot
>>> <vincent.guittot@...aro.org> wrote:
>>>>
>>>> On Fri, 18 Jan 2019 at 11:42, Vincent Guittot
>>>> <vincent.guittot@...aro.org> wrote:
>>>>>
>>>>> Hi Guenter,
>>>>>
>>>>> Le Thursday 17 Jan 2019 à 14:16:28 (-0800), Guenter Roeck a écrit :
>>>>>> On Fri, Dec 21, 2018 at 11:33:56AM +0100, Vincent Guittot wrote:
>>>>>>> From: Thara Gopinath <thara.gopinath@...aro.org>
>>>>>>>
>>>>>>> This patch replaces jiffies based accounting for runtime_active_time
>>>>>>> and runtime_suspended_time with ktime base accounting. This makes the
>>>>>>> runtime debug counters inline with genpd and other pm subsytems which
>>>>>>> uses ktime based accounting.
>>>>>>>
>>>>>>> timekeeping is initialized before pm_runtime_init() so ktime_get() will
>>>>>>> be ready before first call. In fact, timekeeping_init() is called early
>>>>>>> in start_kernel() which is way before driver_init() (and that's when
>>>>>>> devices can start to be initialized) called from rest_init() via
>>>>>>> kernel_init_freeable() and do_basic_setup().
>>>>>>>
>>>>>> This is not (always) correct. My qemu "collie" boot test fails with this
>>>>>> patch applied. Reverting the patch fixes the problem. Bisect log attached.
>>>>>>
>>>>>
>>>>> Can you try the patch below ?
>>>>> ktime_get_mono_fast_ns() has the advantage of being init with dummy clock so
>>>>> it can be used at early_init.
>>>>
>>>> Another possibility would be delay the init of the gpiochip
>>>
>>> Well, right.
>>>
>>> Initializing devices before timekeeping doesn't feel particularly
>>> robust from the design perspective.
>>>
>>> How exactly does that happen?
>>>
>>
>> With an added 'initialized' flag and backtrace into the timekeeping code,
>> with the change suggested earlier applied:
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 0 at kernel/time/timekeeping.c:453 ktime_get_mono_fast_ns+0x114/0x12c
>> Timekeeping not initialized
>> CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc2-next-20190117-dirty #2
>> Hardware name: Sharp-Collie
>> Backtrace:
>> [<c000dce8>] (dump_backtrace) from [<c000df78>] (show_stack+0x18/0x1c)
>>    r7:00000009 r6:00000000 r5:c065ba90 r4:c06d3e54
>> [<c000df60>] (show_stack) from [<c0588930>] (dump_stack+0x20/0x28)
>> [<c0588910>] (dump_stack) from [<c0018ae8>] (__warn+0xcc/0xf4)
>> [<c0018a1c>] (__warn) from [<c0018b5c>] (warn_slowpath_fmt+0x4c/0x6c)
>>    r8:df407b08 r7:00000000 r6:c0c01550 r5:c065bad8 r4:c06dd028
>> [<c0018b14>] (warn_slowpath_fmt) from [<c0069e2c>] (ktime_get_mono_fast_ns+0x114/0x12c)
>>    r3:00000000 r2:c065bad8
>>    r5:00000000 r4:df407b08
>> [<c0069d18>] (ktime_get_mono_fast_ns) from [<c03c7810>] (pm_runtime_init+0x38/0xb8)
>>    r9:c06c9a5c r8:df407b08 r7:00000000 r6:c0c01550 r5:00000000 r4:df407b08
>> [<c03c77d8>] (pm_runtime_init) from [<c03b6a34>] (device_initialize+0xb0/0xec)
>>    r7:00000000 r6:c0c01550 r5:00000000 r4:df407b08
>> [<c03b6984>] (device_initialize) from [<c0366d30>] (gpiochip_add_data_with_key+0x9c/0x884)
>>    r7:00000000 r6:c06fca34 r5:00000000 r4:00000000
>> [<c0366c94>] (gpiochip_add_data_with_key) from [<c06b9708>] (sa1100_init_gpio+0x40/0x98)
>>    r10:dfffcd60 r9:c06c9a5c r8:c06dd020 r7:c06dd028 r6:ffffffff r5:00000000
>>    r4:c06fca34
>> [<c06b96c8>] (sa1100_init_gpio) from [<c06ae58c>] (sa1100_init_irq+0x2c/0x3c)
>>    r7:c06dd028 r6:ffffffff r5:c0713300 r4:c06e1070
>> [<c06ae560>] (sa1100_init_irq) from [<c06aab1c>] (init_IRQ+0x20/0x28)
>>    r5:c0713300 r4:00000000
>> [<c06aaafc>] (init_IRQ) from [<c06a7cd0>] (start_kernel+0x254/0x4cc)
>> [<c06a7a7c>] (start_kernel) from [<00000000>] (  (null))
>>    r10:0000717f r9:6901b119 r8:c0000100 r7:00000092 r6:0000313d r5:00000053
>>    r4:c06a7330
>> ---[ end trace 91e1bd00dd7cce32 ]---
> 
> Does it means that only the pm_runtime_init is done before
> timekeeping_init() but no update_pm_runtime_accounting() ?
> In this case, we can keep using ktimeçget in
> update_pm_runtime_accounting() and find a solution to deal with
> early_call of pm_runtime_init()
> 

For this platform that is correct. I can't answer for the generic case.

Guenter