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

From: "Luck, Tony" <tony.luck@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
	bberg@redhat.com, x86@kernel.org, linux-edac@vger.kernel.org,
	linux-kernel@vger.kernel.org, hdegoede@redhat.com,
	ckellner@redhat.com
Subject: Re: [PATCH 1/2] x86, mce, therm_throt: Optimize logging of thermal throttle messages
Date: Mon, 14 Oct 2019 15:27:35 -0700	[thread overview]
Message-ID: <20191014222735.GA25203@agluck-desk2.amr.corp.intel.com> (raw)
In-Reply-To: <20191014213618.GK4715@zn.tnic>

On Mon, Oct 14, 2019 at 11:36:18PM +0200, Borislav Petkov wrote:
> This description is already *begging* for this delay value to be
> automatically set by the kernel. Putting yet another knob in front of
> the user who doesn't have a clue most of the time shows one more time
> that we haven't done our job properly by asking her to know what we
> already do.
> 
> IOW, a simple history feedback mechanism which sets the timeout based on
> the last couple of values is much smarter. The thing would have a max
> value, of course, which, when exceeded should mean an anomaly, etc, but
> almost anything else is better than merely asking the user to make an
> educated guess.

You need a plausible start point for the "when to worry the user"
message.  Maybe that is your "max value"?

So if the system has a couple of excursions above temperature lasting
1 second and then 2 seconds ... would you like to see those ignored
(because they are below the initial max)? But now we have a couple
of data points pick some new value to be the threshold for reporting?

What value should we pick (based on 1 sec, then 2 sec)?

I would be worried that it would self tune to the point where it
does report something that it really didn't need to (e.g. as a result
of a few consecutive very short excursions).

We also need to take into account the "typical sampling interval"
for user space thermal control software.

Srinivas: Maybe this needs to have some more detail on what user
solutions are being taken into account here.

> > Suggested-by: Alan Cox <alan@linux.intel.com>
> > Commit-comment-by: Tony Luck <tony.luck@intel.com>
>   ^^^^^^^^^^^^^^^^^^
> 
> What's that?

My fault ... during review process I pretty much re-wrote the
whole commit message to follow the form of:
	"What is the problem?"
	"How are we fixing it"
But I didn't want Srinivas to take the heat for any mistakes
that were my fault. "Co-developed-by" really didn't explain
what happened (since I didn't write any code, just made suggestions
on things that needed to be changed/improved).

-Tony