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

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Message-ID: <6e96d2b8-d64c-417c-bbcb-4aa59921c9db@roeck-us.net>
Date:   Wed, 29 Mar 2023 14:49:45 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Zhang, Rui" <rui.zhang@...el.com>
Cc:     "peter.ganzhorn@...il.com" <peter.ganzhorn@...il.com>,
        "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 Wed, Mar 29, 2023 at 02:11:36PM +0000, 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?
> 
Personally I would delete it. I don't see the value of clogging the kernel
log with it.

Guenter