linux-kernel - Re: [RFC] ftrace / perf 'recursion'

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Message-ID: <20160817110448.20b4a6db@gandalf.local.home>
Date:	Wed, 17 Aug 2016 11:04:48 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] ftrace / perf 'recursion'

On Wed, 17 Aug 2016 16:57:09 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> We'd still need the irq_work to wake tasks stuck in poll() and friends.
> And once we're over the watermark, every new event will trigger that
> wakeup, and the wakeup will generate a new event etc..

I just byte the bullet for those (first OS world) issues. If one wants
to trace wake ups, and the wake up of the trace task gets traced, which
causes the trace task to wake up more often, and add more events, then
so be it. I like to see how the tracer affects the system as well. I
noticed that hiding the tracer can make it confusing if one sees gaps
in the trace, where it was the tracer causing it.

-- Steve