linux-kernel - Re: [PATCH v3] tracing: Ignore mmiotrace from kernel commandline

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Date:   Tue, 19 Sep 2017 12:25:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Ziqian SUN (Zamir)" <zsun@...hat.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        karolherbst@...il.com, ppaalanen@...il.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v3] tracing: Ignore mmiotrace from kernel commandline

On Tue, 12 Sep 2017 20:18:35 +0800
"Ziqian SUN (Zamir)" <zsun@...hat.com> wrote:

> >> I feel the core trace printed by WARN is not so meaningful, so I use
> >> pr_warn instead.  
> > 
> > I'm fine with pr_warn, but I'm curious to what you mean by "not so
> > meaningful"? A WARN() will cause a dump stack, which usually shows up
> > as a bug in systems and more likely to be seen. But if someone is
> > adding this to the kernel command line and it's not working, they
> > should be looking for the tracer name within the dmesg anyway.
> >   
> 
> Following is the log I tried with WARN before. With WARN we have both 
> the warning message, and the stack trace. The stack trace goes into 
> stacing_set_tracer, but not showing mmiotrace. I mean, this is useful 
> for debugging, but maybe confusing for users who is willing to report 
> bugs but not a kernel geek. With pr_warn we already indicate mmiotrace 
> is ignored, and is neat.
>

I'm now leaning towards WARN() over pr_warn(). Sure it's more useful
for a kernel geek and not an everyday user, but I will counter that an
everyday user should most definitely not be enabling mmiotrace! Or
other traces for that matter.

But then again, it's not really a bug (it's a feature), so I guess I'll
just take this patch as is.

-- Steve