linux-kernel - Re: [RFC PATCH 16/22 -v2] add get_monotonic

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Date:	Fri, 18 Jan 2008 17:49:19 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	"Frank Ch. Eigler" <fche@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Bird <tim.bird@...sony.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Steven Rostedt <srostedt@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [RFC PATCH 16/22 -v2] add get_monotonic_cycles

On Fri, 18 Jan 2008, Mathieu Desnoyers wrote:
>
> But I have not seen a lot of situations where that kind of glue-code was
> needed, so I think it makes sense to keep markers simple to use and
> efficient for the common case.
>
> Then, in this glue-code, we can put trace_mark() and calls to in-kernel
> tracers.

I'm almost done with the latency tracer work, and there are only a total
of 6 hooks that I needed.

 - schedule context switch
 - try_to_wake_up
 - hard_irqs_off (which is already there for lockdep)
 - hard irqs on (also for lockdep)
 - lock_contention (already in for the lock contention code)
 - lock acquire (also in there for contention code)

With the above, we could have this (if this is what I think you are
recommending). For example in the context_switch case:

	trace_switch_to(prev, next);
	switch_to(prev, next, prev);

and in sched.h I could have:

static inline trace_switch_to(struct task_struct *prev,
			struct task_struct *next)
{
	trace_mark(kernel_schedudule,
		"prev_pid %d next_pid %d prev_state %ld",
		prev->pid, next->pid, prev->pid);

	trace_context_switch(prev, next);
}

and have the trace_context_switch code be something that is turned on with
the latency tracing utility (config option). That way production code can
keep it off.

-- Steve

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