linux-kernel - Re: [PATCH 6/6] tracing/fastboot: Print ktime of sched events when boot tracing

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Date:	Fri, 10 Oct 2008 16:05:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] tracing/fastboot: Print ktime of sched events when
	boot tracing

* Frederic Weisbecker <fweisbec@...il.com> wrote:

> When we use the boot tracer, we want the sched events to be printed 
> with the same timestamp than initcall events. So we have to create a 
> new type of entry which contains sched event attributes and the ktime 
> of the creation of the entry. Then the output is handled by the boot 
> tracer.

hm, i think that's unnecessary duplication. Please extend the context 
switch trace entries to be useful for the boot tracer as well:

> +	entry->time			= ktime_get();

also, ktime_get() can be a quite complex function with dependency on 
xtime_lock - that inverts with the rq lock - so this can lock up 
sporadically when called from within the scheduler.

it would be _much_ simpler to standardize the initcall timestamps on 
cpu_clock() instead. That too is a good global clock and starts at zero 
during bootup. Ok?

Your other patches look good and i've applied them to 
tip/tracing/fastboot:

 3981ce9: tracing/fastboot: use sched switch tracer from boot tracer
 563582a: tracing/ftrace: remove unused code in sched_switch tracer
 d25b1ce: tracing/ftrace: fix a race condition in sched_switch tracer

Thanks,

	Ingo
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