linux-kernel - Re: [PATCH] dynamic debug: allow printing to trace event

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Message-ID: <20200814133415.nbkehai2vp765an5@axis.com>
Date:   Fri, 14 Aug 2020 15:34:15 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     John Ogness <john.ogness@...utronix.de>,
        "jbaron@...mai.com" <jbaron@...mai.com>,
        "mingo@...hat.com" <mingo@...hat.com>, kernel <kernel@...s.com>,
        "corbet@....net" <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH] dynamic debug: allow printing to trace event

On Thu, Jul 23, 2020 at 05:26:44PM +0200, Steven Rostedt wrote:
> On Thu, 23 Jul 2020 12:57:35 +0200
> Vincent Whitchurch <vincent.whitchurch@...s.com> wrote:
> 
> > Would it be acceptable to just use a fixed size for the event?  At least
> > for my own debugging use cases it's preferable to just have to increase
> > the trace buffer size in case it's insufficient, rather than to have to
> > restort to one-off debugging code.
> 
> There's two other options.
> 
> Option 1, is to allocate 256 bytes times 4 (in case of interruption,
> where you have a separate buffer for every context - normal, softirq,
> irq, nmi), and use it like I do for stack traces in the latest kernel
> (see __ftrace_stack_trace() in kernel/trace/trace.c)
> 
> Option 2, would be to use trace_array_vprintk(), but you need to create
> your own instance to do so to keep from messing with the top level buffer.

Thanks for the suggestions, I've sent out a v2 implementing option 1:

https://lore.kernel.org/lkml/20200814133151.7759-1-vincent.whitchurch@axis.com/