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

From: Viktor Rosendahl
Date: Sun May 05 2019 - 19:55:10 EST

On 5/6/19 1:01 AM, Steven Rostedt wrote:
> On Mon, 6 May 2019 00:39:15 +0200
> Viktor Rosendahl <viktor.rosendahl@xxxxxxxxx> 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,