linux-kernel - Re: [PATCHv3 3/3] dynamic_debug: Add a flag for dynamic event tracing

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Date:   Tue, 9 Nov 2021 17:13:13 -0500
From:   Jason Baron <jbaron@...mai.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        quic_psodagud@...cinc.com, Marc Zyngier <maz@...nel.org>,
        gregkh@...uxfoundation.org, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, mingo@...hat.com,
        jim.cromie@...il.com, seanpaul@...omium.org
Subject: Re: [PATCHv3 3/3] dynamic_debug: Add a flag for dynamic event tracing



On 11/9/21 4:51 PM, Steven Rostedt wrote:
> On Tue, 9 Nov 2021 16:42:48 -0500
> Jason Baron <jbaron@...mai.com> wrote:
> 
>> Yeah there is a 'parallel' thread about adding the tracing ring buffer as
>> a 'back end' to the dynamic debug stuff over here:
>> https://urldefense.com/v3/__https://lore.kernel.org/lkml/20211105192637.2370737-9-jim.cromie@gmail.com/__;!!GjvTz_vk!GdVm3olk4hfEx6PjfDDPg4cIbtY60aeqP0IOwu1-S0qJRBZ-OuvC5I_stkqniA$ 
> 
> As the maintainer of tracefs, why am I not Cc'd on that thread :-(
> 
> I'll have to look at that thread later (no time now).
Agreed - that's my bad. I meant to add you earlier in the discussion...

> 
>>
>> The attempt there is more generic but I realize now that it is adding the
>> tracing to an 'instance' which is specific to dynamic debug which is
>> being created via: trace_array_get_by_name(). I would prefer to just have
>> it print to the 'main' trace buffer such that it's easier to read,
>> although I guess they could still be consolidated via timestamps.
>> Hmmm...I think there was a previous proposal to just add a single
>> tracepoint (that takes a string) to the dynamic debug layer that could be
>> called if a dynamic debug site is enabled for trace buffer output. Would
>> that satisfy the ftrace level filtering requirements that you are looking
>> for?
> 
> What we are looking at there is to pass the dynamic debug descriptor to the
> trace event filtering logic, where you could filter on information passed
> to it. For example, on a specific file if a trace event is called by
> several different files or modules.
> 
> -- Steve

Ok, Could this be done at the dynamic debug level as it can already match on specific files and line numbers currently?

Thanks,

-Jason