From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 3/6] dax: add tracepoint infrastructure, PMD tracing
Date: Sun, 27 Nov 2016 16:58:43 -0800
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Cc: Al Viro <viro@zeniv.linux.org.uk>, Ross Zwisler <ross.zwisler@linux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>, Dan Williams <dan.j.williams@intel.com>, Ingo Molnar <mingo@redhat.com>,
	Jan Kara <jack@suse.cz>, Matthew Wilcox <mawilcox@microsoft.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
To: Dave Chinner <david@fromorbit.com>
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On Sun, Nov 27, 2016 at 2:42 PM, Dave Chinner <david@fromorbit.com> wrote:
>
> And that's exactly why we need a method of marking tracepoints as
> stable. How else are we going to know whether a specific tracepoint
> is stable if the kernel code doesn't document that it's stable?

You are living in some unrealistic dream-world where you think you can
get the right tracepoint on the first try.

So there is no way in hell I would ever mark any tracepoint "stable"
until it has had a fair amount of use, and there are useful tools that
actually make use of it, and it has shown itself to be the right
trace-point.

And once that actually happens, what's the advantage of marking it
stable? None. It's a catch-22. Before it has uses and has been tested
and found to be good, it's not stable. And after, it's pointless.

So at no point does such a "stable" tracepoint marking make sense. At
most, you end up adding a comment saying "this tracepoint is used by
tools such-and-such".

                   Linus

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