linux-kernel - Re: [PATCH] ftrace: add ftrace_graph_max

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Date:   Thu, 2 Mar 2017 20:09:50 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Todd Brandt <todd.e.brandt@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, todd.e.brandt@...el.com
Subject: Re: [PATCH] ftrace: add ftrace_graph_max_depth kernel parameter

On Thu, 02 Mar 2017 16:54:57 -0800
Todd Brandt <todd.e.brandt@...ux.intel.com> wrote:

> BTW I had one other question for you, is it possible to move the ftrace
> module's initialization further up the queue? ATM it initializes at
> about 600ms into boot, which is fine since most of the performance
> issues are happening at 1000ms+. But eventually it might be nice to
> trace some of the earlier init code.

module initialization? Or you mean boot up initialization?

For boot up, we have this:

	mm_init();
	sched_init();
	idr_init_cache();
	workqueue_init_early();
	rcu_init();
	trace_init();

Now, going before mm_init() will definitely be quite a pain, as we
that would require making the ring buffer out of early boot memory.

We could add a early_trace_init() just before sched_init(), with some
limited tracing. Tracepoints require rcu, although we could make hooks
to just do hard coded changes (no rcu synchronization) with a flag that
denotes that trace_init() hasn't been called yet.

I could toy with the idea, implement it, and see what breaks.

-- Steve