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Date:   Wed, 9 Feb 2022 10:09:08 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Byungchul Park <byungchul.park@lge.com>,
        "Paul E. McKenney" <paul.mckenney@linaro.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Radoslaw Burny <rburny@google.com>, Tejun Heo <tj@kernel.org>,
        rcu@vger.kernel.org, cgroups@vger.kernel.org,
        linux-btrfs@vger.kernel.org, intel-gfx@lists.freedesktop.org
Subject: Re: [RFC 00/12] locking: Separate lock tracepoints from
 lockdep/lock_stat (v1)
Message-ID: <20220209090908.GK23216@worktop.programming.kicks-ass.net>
References: <20220208184208.79303-1-namhyung@kernel.org>
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On Tue, Feb 08, 2022 at 10:41:56AM -0800, Namhyung Kim wrote:

> Eventually I'm mostly interested in the contended locks only and I
> want to reduce the overhead in the fast path.  By moving that, it'd be
> easy to track contended locks with timing by using two tracepoints.

So why not put in two new tracepoints and call it a day?

Why muck about with all that lockdep stuff just to preserve the name
(and in the process continue to blow up data structures etc..). This
leaves distros in a bind, will they enable this config and provide
tracepoints while bloating the data structures and destroying things
like lockref (which relies on sizeof(spinlock_t)), or not provide this
at all.

Yes, the name is convenient, but it's just not worth it IMO. It makes
the whole proposition too much of a trade-off.

Would it not be possible to reconstruct enough useful information from
the lock callsite?