linux-kernel - Re: [PATCH v1] thermal/core: change mm alloc method to avoid kernel warning

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Date:   Tue, 19 Apr 2022 19:56:35 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Zhang Rui <rui.zhang@...el.com>, Junwen Wu <wudaemon@....com>,
        rafael@...nel.org, amitk@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH v1] thermal/core: change mm alloc method to avoid kernel
 warning

On 19/04/2022 15:54, Zhang Rui wrote:
> CC Viresh.
> 
> On Tue, 2022-04-19 at 11:14 +0200, Daniel Lezcano wrote:
>> On 19/04/2022 10:48, Zhang Rui wrote:
>>> On Sun, 2022-04-17 at 12:56 +0000, Junwen Wu wrote:
>>>> Very high cooling device max state value makes cooling device
>>>> stats
>>>> buffer allocation fails,like below.Using kzvalloc instead of
>>>> kzalloc
>>>> can avoid this issue.
>>>
>>> When a cooling device has big max_state, this patch can get ride of
>>> the
>>> warning here, but still we end up with the read failure of the
>>> trans_table in sysfs because it is larger than PAGE_SIZE.
>>>
>>> $ cat /sys/class/thermal/cooling_device8/stats/trans_table
>>> cat: /sys/class/thermal/cooling_device8/stats/trans_table: File too
>>> large
>>>
>>> IMO, unless we can fix both places, I'd suggest we skip allocating
>>> and
>>> creating the broken trans_table attr. Like a prototype patch below
>>
>> Why not create a thermal debugfs with real useful information and
>> get
>> rid of this broken code ?
> 
> The idea looks good to me.

What about doing a percentile approach of the state indexes changes 
instead of a raw matrix full of zeros ? So we show the most significant 
transitions, perhaps something like:

99%:	7->6	6->7
98%:	6->5	5->6
95%:	5->4	4->5
90%:	7->5	5->7
80%:	6->4	4->6
70%:	7->1	7->2
50%:	...	...

total:	123456	124573


And another statistics file containing some timings information like the 
total duration in mitigation, and the duration in the most significant 
states above?

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