linux-kernel - Re: [PATCHv2 1/1] perf/x86/intel: make error messages less confusing

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Message-ID: <20180914000050.GI16020@u40b0340c692b58f6553c.ant.amazon.com>
Date:   Thu, 13 Sep 2018 17:00:50 -0700
From:   Eduardo Valentin <eduval@...zon.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Andi Kleen <ak@...ux.intel.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "Jia Zhang" <qianyue.zj@...baba-inc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 1/1] perf/x86/intel: make error messages less confusing

Hey Peter,

On Thu, Sep 06, 2018 at 09:21:49AM +0200, Peter Zijlstra wrote:
> On Wed, Sep 05, 2018 at 02:47:07PM -0700, Andi Kleen wrote:
> > On Wed, Sep 05, 2018 at 08:53:17AM -0700, Eduardo Valentin wrote:
> > > On Wed, Sep 05, 2018 at 10:52:12AM +0200, Peter Zijlstra wrote:
> > > > On Thu, Aug 23, 2018 at 08:07:32AM -0700, Eduardo Valentin wrote:
> > > > > On a system with X86_FEATURE_ARCH_PERFMON disabled
> > > > > and with a model not known by family PMU drivers,
> > > > > user gets a kernel message log like the following:
> > > > > [ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.
> > > > > 
> > > > > The "unsupported .. CPU" part may be confusing for some
> > > > > users leading to wrong understanding that the kernel
> > > > > does not support the CPU model.
> > > > 
> > > > Send them back to first grade, such that they might learn to read?
> > > > 
> > > 
> > > :-)
> > 
> > I think it's a valid concern, I guess Eduardo actually has real people
> > who got confused.
> 
> But it is really easy to confuse real people; as real people are mostly
> clueless.  There is only so much you can do for the semi illiterate
> masses. Should we dumb down everything to baby talk just to cater to
> them?
> 
> The string is clearly prefixed by the subsystem, if you get confused by
> that your reading comprehension really is rock bottom.
> 
>   [ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.
> 

Once again, the confusing part is the "unsupported CPU".

> Heck, it even mentions "no PMU driver", how much clues do you need?
> Also, the proposed alternative:
> 
>   [ 0.667154] Performance Events: CPU does not support PMU: no PMU driver, software events only.
> 
> Looses out information on which CPU family we failed on. Nor does it


Maybe keeping the CPU family and rephrasing the unsupported part?

> mention the most likely reason for this error: virt crap.
> 
> I'd not mind a warning like:
> 
>   [] Performance Events: Your crappy virt solution is lying about it's CPU model, it doesn't have a (matching) PMU.
> 

Well, I would be OK if the kernel spits out a message saying that vPMU is disabled or something.
That would be more accurate than unsupported CPU.

> 
> 

-- 
All the best,
Eduardo Valentin