linux-kernel - Re: [PATCH 0/4] coretemp: Fix spamming of ring buffer

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Message-ID: <881c4859-db85-b36c-de11-1552ba7e6ff4@gmail.com>
Date:   Wed, 29 Mar 2023 20:53:19 +0200
From:   Peter Ganzhorn <peter.ganzhorn@...il.com>
To:     "Zhang, Rui" <rui.zhang@...el.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>
Cc:     "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] coretemp: Fix spamming of ring buffer

On 3/29/23 16:11, Zhang, Rui wrote:
> On Wed, 2023-03-29 at 05:47 -0700, Guenter Roeck wrote:
>> On Wed, Mar 29, 2023 at 03:43:58AM +0000, Zhang, Rui wrote:
>>> Hi, Peter,
>>>
>>> CC the list.
>>>
>>> On Tue, 2023-03-28 at 22:37 +0200, Peter Ganzhorn wrote:
>>>> Dear Mr. Rui,
>>>> Dear Mr. Roeck,
>>>>
>>>> please consider accepting the attached patches or
>>>> modifying the coretemp code to stop spamming my syslog.
>>>> I would appreciate it very much if you can accept the patches.
>>>>
>>>> coretemp: Improve dynamic changes of TjMax
>>>> After introduction of dynamic TjMax changes in commit
>>>> c0c67f8761cec1fe36c21d85b1a5400ea7ac30cd
>>>> my syslog gets spammed with "TjMax is ... degrees C"
>>>> messages.
>>>> If TjMax is subject to change at any time, it won't be
>>>> set in tdata anymore and re-read every time from MSR.
>>>> This causes quite a lot of dev_dbg() messages to be issued.
>>>>
>>>> The following patches change the code to read TjMax
>>>> from the MSRs into tdata->tjmax (again) but allow for a
>>>> dynamic update at any time as well. (Patches 1 and 2)
>>>> This way a message will only be issued after actual changes.
>>>> Also I replaced the dev_dbg() with dev_notice (Patch 3) and
>>>> added a additional dev_notice for the case where TjMax is
>>>> set based on assumptions. (Patch 4)
>>>>
>>>>
>>>> If you do not want to accept my patches, removing the
>>>> dev_dbg() in get_tjmax() would be the most simple
>>>> solution I guess.
>>>>
>>> Please check if below patch solves your problem or not.
>>>
>>>  From 9370ee5163a85f65230b5222f1f4dece59ce078a Mon Sep 17 00:00:00
>>> 2001
>>> From: Zhang Rui <rui.zhang@...el.com>
>>> Date: Wed, 29 Mar 2023 11:35:18 +0800
>>> Subject: [PATCH] hwmon: (coretemp) Avoid duplicate debug messages
>>>
>>> Avoid duplicate dev_dbg messages when tjmax value retrieved from
>>> MSR
>>> does not change.
>>>
>>> Signed-off-by: Zhang Rui <rui.zhang@...el.com>
>>> ---
>>>   drivers/hwmon/coretemp.c | 6 +++++-
>>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
>>> index 30d77f451937..809456967b50 100644
>>> --- a/drivers/hwmon/coretemp.c
>>> +++ b/drivers/hwmon/coretemp.c
>>> @@ -267,6 +267,7 @@ static int get_tjmax(struct temp_data *tdata,
>>> struct device *dev)
>>>   	int err;
>>>   	u32 eax, edx;
>>>   	u32 val;
>>> +	static u32 tjmax;
>> That would apply to every instance of this driver, meaning to every
>> CPU core. Is that really appropriate ?
>>
>> Guenter
>>
> Good point.
>
> MSR_IA32_TEMPERATURE_TARGET is package scope, and the cached tjmax
> should also be package scope, or else this message is shown for each
> cpu when tjmax changes in one package.
>
> Previously, the message is printed only once during driver probing time
> thus I'm wondering how useful this is.
>
> Maybe we can just delete it?
>
> thanks,
> rui
The proposed patch from Rui Zhang does solve the issue of spamming the 
syslog.

I only get one message at boot:

[    1.370790] platform coretemp.0: TjMax is 96 degrees C

But if different packages have different tjmax values I guess the 
spamming issue may return.

Personally I'd prefer to get a message once if tjmax changes for any 
package.

Thank you both for the quick reaction.
Peter