linux-kernel - Re: [PATCH v1] arch/x86: port I/O tracing on x86

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Message-ID: <a5c505d1-730c-912c-3c83-1df83d8e264b@foxvalley.net>
Date:   Tue, 19 Sep 2023 13:56:15 -0600
From:   Dan Raymond <draymond@...valley.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com
Subject: Re: [PATCH v1] arch/x86: port I/O tracing on x86

> No, very much no.
> 
> This sticks tracing in the very rawest of raw output paths.

That's the point.  Tracing is a low level debug tool that can be
used to debug the kernel itself.  If you don't trace all port I/O
then you are bound to miss something important while debugging.

> This means I can no longer use early_console->write() to print to my
> early_serial_console.

Why not?  Did you try it?

> That is the one and only fully reliably output path we have. You're not
> sticking tracing in it.

Keep in mind that tracing is optional.  It can be turned off using
CONFIG_TRACEPOINTS.