linux-kernel - Re: [PATCH V3 9/9] tracing: Add timerlat tracer

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Date:   Sat, 12 Jun 2021 19:06:41 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Kate Carcia <kcarcia@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Clark Willaims <williams@...hat.com>,
        John Kacur <jkacur@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH V3 9/9] tracing: Add timerlat tracer

On Sat, 12 Jun 2021 11:41:41 +0200
Daniel Bristot de Oliveira <bristot@...hat.com> wrote:
> > I think the above may be easier to understand, especially if the trace
> > output that represents it is below.  
> 
> ok, I can try to capture a trace sample and represent it into the ASCII art
> format above.

Why capture it? Just fudge an example that fits the example ;-)

> 
> > Also, I have to ask, shouldn't the "thread noise" really start at the
> > "External clock event"?  
> 
> To go in that direction, we need to track things that delayed the IRQ execution.

[snip long explanation of the obvious (to me at least) ;-) ]

> the overhead is acceptable because of the sound analysis of the scheduling bound
> (which is rooted in a formal specification & analysis of the system).

I meant, that it needs to be documented, what the real thread noise is
but due to what is available it may not be truly accurate.

-- Steve