linux-kernel - Re: [PATCH v2 1/4] ftrace: Implement fs notification for preempt/irqsoff tracers

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Date:   Sun, 5 May 2019 15:43:33 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Viktor Rosendahl <viktor.rosendahl@...il.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] ftrace: Implement fs notification for
 preempt/irqsoff tracers

On Sat, 4 May 2019 12:47:10 -0400
Joel Fernandes <joel@...lfernandes.org> wrote:

 
> I agree with the general idea, but I don't really like how it is done in the
> patch.

+1

> 
> We do have a notification mechanism already in the form of trace_pipe. Can we
> not improve that in some way to be notified of a new trace data? In theory,
> the trace_pipe does fit into the description in the documentation: "Reads
> from this file will block until new data is retrieved"
> 
> More comment below:
> 
> 

> > +	config PREEMPTIRQ_FSNOTIFY
> > +	bool "Generate fsnotify events for the latency tracers"
> > +	default n
> > +	depends on (IRQSOFF_TRACER || PREEMPT_TRACER) && FSNOTIFY
> > +	help
> > +	  This option will enable the generation of fsnotify events for the
> > +	  trace file. This makes it possible for userspace to be notified about
> > +	  modification of /sys/kernel/debug/tracing/trace through the inotify
> > +	  interface.  
> 
> Does this have to be a CONFIG option? If prefer if the code automatically
> does the notification and it is always enabled. I don't see any drawbacks of
> that.

I mentioned that anything it needs to be an option.


> > +#ifdef CONFIG_PREEMPTIRQ_FSNOTIFY
> > +
> > +static void trace_notify_workfn(struct work_struct *work)  
> [snip]
> 
> I prefer if this facility is available to other tracers as well such as
> the wakeup tracer which is similar in output (check
> Documentation/trace/ftrace.txt). I believe this should be a generic trace
> facility, and not tracer specific.


For what it's worth, I agree with everything Joel just stated.

Thanks,

-- Steve