linux-kernel - Re: [PATCH 2/4] tracing: add event trace infrastructure

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Message-ID: <alpine.DEB.2.00.0902251746080.12697@gandalf.stny.rr.com>
Date:	Wed, 25 Feb 2009 17:48:06 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Pekka Paalanen <pq@....fi>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jason Baron <jbaron@...hat.com>,
	Martin Bligh <mbligh@...gle.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/4] tracing: add event trace infrastructure



On Wed, 25 Feb 2009, Ingo Molnar wrote:

> 
> * Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > > #                _------=> CPU#
> > > #               / _-----=> irqs-off
> > > #              | / _----=> need-resched
> > > #              || / _---=> hardirq/softirq
> > > #              ||| / _--=> preempt-depth
> > > #              |||| /
> > > #              |||||     delay
> > > #  cmd     pid ||||| time  |   caller
> > > #     \   /    |||||   \   |   /
> > >   <idle>-0     0d..1    0us+: trace_hardirqs_off_thunk (apic_timer_interrupt)
> > >   <idle>-0     0d.s.   97us : __do_softirq (do_softirq)
> > >   <idle>-0     0d.s1   98us : trace_hardirqs_on (do_softirq)
> [...]
> > > 
> > > your time starts now.
> > 
> > Note, that is a legacy format, that works great for the 
> > latency tracers. Those include (the example you used) irqsoff, 
> > the preempt off, wake up latencies. This gives us a nice 
> > listing of why we are hitting a latency. All other plugins 
> > generally use the trace file, although they could also use 
> > that file too.
> > 
> > As for your English comment. I showed the header to my wife, 
> > and she had no idea what irqs-off means, nor need-resched, nor 
> > preempt-depth ;-) They are not quite English as they are 
> > technical terms. Most of the names are hard coded into the 
> > kernel too.
> > 
> > Yeah, maybe that file (latency_trace) is a bit too much. I for 
> > one love it. It is great to load a kernel on some remote box, 
> > and run the irqs off latency tracer to see where the 
> > interrupts are disabled for the longest time. This format is 
> > really nice because it shows me when we are in an interrupt, 
> > or interrupts are disabled, and when the task should have been 
> > rescheduled.
> > 
> > This has help find places that we miss a preemption check too.
> 
> Could we get that, as PeterZ has suggested, as a trace_option 
> column in the 'trace' file? It would be default off for 
> non-latency tracers, with latency tracing plugins turning it on 
> by default. Would that work?

I guess adding options will be a high priority for me now. I can't parse 
irqsoff output anymore :-(

Besides the information of the ..... area, the times were all based off of 
the start of the trace, not global. This allowed you to see the latency in 
the trace.

-- Steve

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