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Date:   Wed, 5 Jun 2019 09:22:27 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Qais Yousef <qais.yousef@arm.com>, Ingo Molnar <mingo@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-kernel@vger.kernel.org,
        Pavankumar Kondeti <pkondeti@codeaurora.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Uwe Kleine-Konig <u.kleine-koenig@pengutronix.de>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Quentin Perret <quentin.perret@arm.com>
Subject: Re: [PATCH v3 0/6] sched: Add new tracepoints required for EAS
 testing
Message-ID: <20190605072227.GI3419@hirez.programming.kicks-ass.net>
References: <20190604111459.2862-1-qais.yousef@arm.com>
 <20190605061748.GA20661@infradead.org>
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On Tue, Jun 04, 2019 at 11:17:48PM -0700, Christoph Hellwig wrote:
> > The following patches add the bare minimum tracepoints required to perform EAS
> > testing in Lisa[1].
> 
> What is EAS?  Whhy is "Lisa" not part of the patch submission?
> submission.
> 
> > It is done in this way because adding new TRACE_EVENTS() is no longer accepted
> > AFAIU.
> 
> Huh?  We keep adding trace events all the time.  And they actually
> are useful because they are testable.

They also form an implicit API/ABI with userspace, and I've been bitten
by that crap before. No more tracepoints. IIRC viro is also not having
tracepoints in the vfs.

> This series on the other hand adds exports not used in tree, which is
> a big no-go.

I much prefer a few unused exports that expose data in a controlled
fashion than commit to an implicit ABI through tracepoints. By keeping
it all in kernel, we're punting to the no-in-kernel-ABI rule.

Basically nobody gives a crap if we break (out-of-tree) modules, but the
moment we break something userspace we're fscked.