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SubjectRe: [PATCH 2/4] tracing: add event trace infrastructure
On Wed, 25 Feb 2009 11:33:07 +0200 Pekka Enberg <penberg@cs.helsinki.fi> wrote:

> Hi Andrew,
>
> On Wed, 2009-02-25 at 01:22 -0800, Andrew Morton wrote:
> > irqsoff latency trace v1.1.5 on 2.6.26-rc8
> > --------------------------------------------------------------------
> > latency: 97 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
> > -----------------
> > | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0)
> > -----------------
> > => started at: apic_timer_interrupt
> > => ended at: do_softirq
>
> <the header seems broken here, should have # at the beginning of the line>
>
> >
> > # _------=> 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.
>
> Well, what do you want to know? The first thing to do here is to:
>
> $ grep -v "#" trace
> <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)
>
> after which you have access to the raw data. This particular trace seems
> to be somewhat hard to parse (because not all fields are whitespace
> delimited) but I can assure you that any format I rely on is not.

yes, but now you need to think about how this interface would have been
designed if we'd decided to access it with something smarter than
`cat'.

I mean, look at it. All the multi-space column lining upping, the
unnecessary "us" annotation, the strange symbol(symbol) thing, etc.
Plus it would have been more self-describing. Right now, your parser
has to either assume that the second character of "0d..1" is
"irqs-off", or it has to learn how to follow ascii art lines.

Plus... it's all English-only.

> So if you're arguing against specific ftrace plugins, go ahead (you
> probably have a fair point there). But please don't dismiss the while
> _concept_ of ftrace because of them.

Where on earth did that come from?

What I'm arguing against is putting English-only pretty-printers and
pretty-parsers on wrong side of int 80. That's all.



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