linux-kernel - Re: [PATCH 1/2] x86, mce, therm_throt: Optimize logging of thermal throttle messages

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Date:   Wed, 16 Oct 2019 10:14:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     tony.luck@...el.com, bp@...en8.de, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, bberg@...hat.com, x86@...nel.org,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        hdegoede@...hat.com, ckellner@...hat.com
Subject: Re: [PATCH 1/2] x86, mce, therm_throt: Optimize logging of thermal
 throttle messages

On Tue, Oct 15, 2019 at 06:31:46AM -0700, Srinivas Pandruvada wrote:
> On Tue, 2019-10-15 at 10:48 +0200, Peter Zijlstra wrote:
> > On Mon, Oct 14, 2019 at 02:21:00PM -0700, Srinivas Pandruvada wrote:
> > > Some modern systems have very tight thermal tolerances. Because of
> > > this
> > > they may cross thermal thresholds when running normal workloads
> > > (even
> > > during boot). The CPU hardware will react by limiting
> > > power/frequency
> > > and using duty cycles to bring the temperature back into normal
> > > range.
> > > 
> > > Thus users may see a "critical" message about the "temperature
> > > above
> > > threshold" which is soon followed by "temperature/speed normal".
> > > These
> > > messages are rate limited, but still may repeat every few minutes.
> > > 
> > > The solution here is to set a timeout when the temperature first
> > > exceeds
> > > the threshold.
> > 
> > Why can we even reach critical thresholds when the fans are working?
> > I
> > always thought it was BAD to ever reach the critical temps and have
> > the
> > hardware throttle.
> CPU temperature doesn't have to hit max(TjMax) to get these warnings.
> OEMs has an ability to program a threshold where a thermal interrupt
> can be generated. In some systems the offset is 20C+ (Read only value).
> 
> In recent systems, there is another offset on top of it which can be
> programmed by OS, once some agent can adjust power limits dynamically.
> By default this is set to low by the firmware, which I guess the prime
> motivation of Benjamin to submit the patch.

That all sounds like the printk should be downgraded too, it is not a
KERN_CRIT warning. It is more a notification that we're getting warm.