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

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Date:   Mon, 6 May 2019 01:54:04 +0200
From:   Viktor Rosendahl <viktor.rosendahl@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        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 5/6/19 1:01 AM, Steven Rostedt wrote:
 > On Mon,  6 May 2019 00:39:15 +0200
 > Viktor Rosendahl <viktor.rosendahl@...il.com> wrote:
 >
 >> Can you explain more precisely what you agree with?
 >>
 >> The general idea of being able to trace bursts of latencies?
 >
 > One thing I have an issue with the current approach is the use of the
 > trace file for this.

You mean that using fsnotify is kind of okayish but that it's confusing 
for the
user because only a subset of tracers would send the fsnotify event when the
trace file is updated?

 >
 > Hmm, what about adding a notifier to tracing_max_latency instead? And
 > do it not as a config option, but have it always enabled. It would send a
 > notification when it changes, and that only happens when there's a new
 > max latency. Would that work for you?

Yes, it seems to be OK since the tracing_max_latency is updated also
with the latest latency that exceeds the threshold when we are using
tracing_thresh. I will try to send a new version of the patch series
soon, with the modifications that have been discussed so far.

best regards,

Viktor