linux-kernel - Re: [PATCH] tracing: Add bitmask-list option for human-readable bitmask display

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Message-ID: <qw6wgsrmuu4vhuam3ay3zdsqxlowbe7xqrh3wolei7bnbkkwyw@jshbmlr67goc>
Date: Thu, 25 Dec 2025 02:38:03 -0500
From: Aaron Tomlin <atomlin@...mlin.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: mhiramat@...nel.org, mark.rutland@....com, 
	mathieu.desnoyers@...icios.com, corbet@....net, sean@...e.io, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] tracing: Add bitmask-list option for human-readable
 bitmask display

On Wed, Dec 24, 2025 at 08:58:48AM -0500, Steven Rostedt wrote:
> Should we just make all cpu bitmask range lists instead?

Hi Steve,

I am somewhat hesitant to adopt that suggestion as I would prefer to avoid
breaking any existing tooling that relies upon the default hexadecimal
bitmask format.

Whilst range lists are undoubtedly superior for human interpretation, the
hexadecimal output is a well-established standard throughout the kernel.
For instance, the hexadecimal format is still strictly adhered to for
"Cpus_allowed:" within /proc/[pid]/status. Introducing a global change to
ftrace defaults could disrupt parsers and scripts that expect this
consistency across the system.

By leveraging the existing bitmask-list trace option via
trace_print_bitmask_seq(), we offer users the requisite flexibility for
high-core-count systems whilst preserving backward compatibility for the
wider ecosystem.

I shall send a new version of the patch shortly. This version incorporates
the use of iter->tmp_seq to ensure the implementation is robust,
instance-aware, and free from buffer contention or duplication issues.

Kind regards,
-- 
Aaron Tomlin

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