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	Tue, 12 May 2026 07:48:47 +0000
Date: Tue, 12 May 2026 00:48:39 -0700
From: Breno Leitao <leitao@debian.org>
To: Gustavo Luiz Duarte <gustavold@gmail.com>
Cc: Joel Fernandes <joelagnelf@nvidia.com>, 
	"Paul E. McKenney" <paulmck@kernel.org>, Frederic Weisbecker <frederic@kernel.org>, 
	Neeraj Upadhyay <neeraj.upadhyay@kernel.org>, Josh Triplett <josh@joshtriplett.org>, 
	Boqun Feng <boqun@kernel.org>, Uladzislau Rezki <urezki@gmail.com>, 
	Steven Rostedt <rostedt@goodmis.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 
	Lai Jiangshan <jiangshanlai@gmail.com>, Zqiang <qiang.zhang@linux.dev>, 
	Vlastimil Babka <vbabka@kernel.org>, Harry Yoo <harry@kernel.org>, 
	Andrew Morton <akpm@linux-foundation.org>, Hao Li <hao.li@linux.dev>, Christoph Lameter <cl@gentwo.org>, 
	David Rientjes <rientjes@google.com>, Roman Gushchin <roman.gushchin@linux.dev>, rcu@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH RFC 0/2] rcu: Add debugfs interface for pending callback
 monitoring
Message-ID: <agLaaBslalzcWhhH@gmail.com>
References: <20260507-rcu-pending-cbs-stats-v1-0-8f4eb3553bc9@gmail.com>
 <fd8b4470-930b-4688-b423-2e349f8c883f@nvidia.com>
 <CAGSyskW6T4cbX53gSRZSGeiTct9zHLBo9vsE9OH3Yw_sB1Frfg@mail.gmail.com>
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X-Debian-User: leitao

On Mon, May 11, 2026 at 06:08:53PM +0100, Gustavo Luiz Duarte wrote:
> > You actually don't need debugfs for this. You can just use bpftrace and
> > instrument trace_rcu_ (with other RCU tracing Kconfig options enabled?). I had
> > something like that working sometime ago.
>
> My initial attempt to do this using tracepoints was probing
> trace_rcu_segcb_stats, but this would add significant overhead to
> every callback enqueue/dequeue event which is too expensive for a
> production environment

An additional benefit of this debugfs-based approach is that it eliminates
the dependency on bpftrace and custom scripts. While instrumenting tracepoints
with bpftrace is certainly feasible for a limited number of servers, deploying
it fleet-wide becomes problematic. It requires distributing and maintaining
additional binaries on every host, just to collect metrics that a few lines
of kernel code can expose more efficiently.

So while bpftrace can technically accomplish this, it may not be the
most appropriate solution for this particular use case.