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SubjectRe: [PATCH v3 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver
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On 05/08/2019 08:53, Martin Kepplinger wrote:

[ ... ]

>>> +static s64 cpuidle_cooling_runtime(struct cpuidle_cooling_device *idle_cdev)
>>> +{
>>> + s64 next_wakeup;
>>> + unsigned long state = idle_cdev->state;
>>> +
>>> + /*
>>> + * The function should not be called when there is no
>>> + * mitigation because:
>>> + * - that does not make sense
>>> + * - we end up with a division by zero
>>> + */
>>> + if (!state)
>>> + return 0;
>>> +
>>> + next_wakeup = (s64)((idle_cdev->idle_cycle * 100) / state) -
>>> + idle_cdev->idle_cycle;
>>> +
>>> + return next_wakeup * NSEC_PER_USEC;
>>> +}
>>> +
>>
>> There is a bug in your calculation formula here when "state" becomes 100.
>> You return 0 for the injection rate, which is the same as "rate" being 0,
>> which is dangerous. You stop cooling when it's most necessary :)
>>
>> I'm not sure how much sense really being 100% idle makes, so I, when testing
>> this, just say if (state == 100) { state = 99 }. Anyways, just don't return 0.
>>
>
> oh and also, this breaks S3 suspend:

What breaks the S3 suspend? The idle cooling device or the bug above ?

> Aug 5 06:09:20 pureos kernel: [ 807.487887] PM: suspend entry (deep)
> Aug 5 06:09:40 pureos kernel: [ 807.501148] Filesystems sync: 0.013
> seconds
> Aug 5 06:09:40 pureos kernel: [ 807.501591] Freezing user space
> processes ... (elapsed 0.003 seconds) done.
> Aug 5 06:09:40 pureos kernel: [ 807.504741] OOM killer disabled.
> Aug 5 06:09:40 pureos kernel: [ 807.504744] Freezing remaining
> freezable tasks ...
> Aug 5 06:09:40 pureos kernel: [ 827.517712] Freezing of tasks failed
> after 20.002 seconds (4 tasks refusing to freeze, wq_busy=0):
> Aug 5 06:09:40 pureos kernel: [ 827.527122] thermal-idle/0 S 0
> 161 2 0x00000028
> Aug 5 06:09:40 pureos kernel: [ 827.527131] Call trace:
> Aug 5 06:09:40 pureos kernel: [ 827.527148] __switch_to+0xb4/0x200
> Aug 5 06:09:40 pureos kernel: [ 827.527156] __schedule+0x1e0/0x488
> Aug 5 06:09:40 pureos kernel: [ 827.527162] schedule+0x38/0xc8
> Aug 5 06:09:40 pureos kernel: [ 827.527169] smpboot_thread_fn+0x250/0x2a8
> Aug 5 06:09:40 pureos kernel: [ 827.527176] kthread+0xf4/0x120
> Aug 5 06:09:40 pureos kernel: [ 827.527182] ret_from_fork+0x10/0x18
> Aug 5 06:09:40 pureos kernel: [ 827.527186] thermal-idle/1 S 0
> 162 2 0x00000028
> Aug 5 06:09:40 pureos kernel: [ 827.527192] Call trace:
> Aug 5 06:09:40 pureos kernel: [ 827.527197] __switch_to+0x188/0x200
> Aug 5 06:09:40 pureos kernel: [ 827.527203] __schedule+0x1e0/0x488
> Aug 5 06:09:40 pureos kernel: [ 827.527208] schedule+0x38/0xc8
> Aug 5 06:09:40 pureos kernel: [ 827.527213] smpboot_thread_fn+0x250/0x2a8
> Aug 5 06:09:40 pureos kernel: [ 827.527218] kthread+0xf4/0x120
> Aug 5 06:09:40 pureos kernel: [ 827.527222] ret_from_fork+0x10/0x18
> Aug 5 06:09:40 pureos kernel: [ 827.527226] thermal-idle/2 S 0
> 163 2 0x00000028
> Aug 5 06:09:40 pureos kernel: [ 827.527231] Call trace:
> Aug 5 06:09:40 pureos kernel: [ 827.527237] __switch_to+0xb4/0x200
> Aug 5 06:09:40 pureos kernel: [ 827.527242] __schedule+0x1e0/0x488
> Aug 5 06:09:40 pureos kernel: [ 827.527247] schedule+0x38/0xc8
> Aug 5 06:09:40 pureos kernel: [ 827.527259] smpboot_thread_fn+0x250/0x2a8
> Aug 5 06:09:40 pureos kernel: [ 827.527264] kthread+0xf4/0x120
> Aug 5 06:09:40 pureos kernel: [ 827.527268] ret_from_fork+0x10/0x18
> Aug 5 06:09:40 pureos kernel: [ 827.527272] thermal-idle/3 S 0
> 164 2 0x00000028
> Aug 5 06:09:40 pureos kernel: [ 827.527278] Call trace:
> Aug 5 06:09:40 pureos kernel: [ 827.527283] __switch_to+0xb4/0x200
> Aug 5 06:09:40 pureos kernel: [ 827.527288] __schedule+0x1e0/0x488
> Aug 5 06:09:40 pureos kernel: [ 827.527293] schedule+0x38/0xc8
> Aug 5 06:09:40 pureos kernel: [ 827.527298] smpboot_thread_fn+0x250/0x2a8
> Aug 5 06:09:40 pureos kernel: [ 827.527303] kthread+0xf4/0x120
> Aug 5 06:09:40 pureos kernel: [ 827.527308] ret_from_fork+0x10/0x18
> Aug 5 06:09:40 pureos kernel: [ 827.527375] Restarting kernel threads
> ... done.
> Aug 5 06:09:40 pureos kernel: [ 827.527771] OOM killer enabled.
> Aug 5 06:09:40 pureos kernel: [ 827.527772] Restarting tasks ... done.
> Aug 5 06:09:40 pureos kernel: [ 827.528926] PM: suspend exit
>
>
> do you know where things might go wrong here?
>
> thanks,
>
> martin
>


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