linux-kernel - Re: [PATCH -tip v5 0/7] tracing: kprobe-based event tracer and x86 instruction decoder

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Date:	Mon, 11 May 2009 23:47:12 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>, Avi Kivity <avi@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Jim Keniston <jkenisto@...ibm.com>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	systemtap <systemtap@...rces.redhat.com>,
	kvm <kvm@...r.kernel.org>, Tom Zanussi <zanussi@...cast.net>
Subject: Re: [PATCH -tip v5 0/7] tracing: kprobe-based event tracer and x86
	instruction decoder


* Masami Hiramatsu <mhiramat@...hat.com> wrote:

> Steven Rostedt wrote:
> > On Mon, 11 May 2009, Masami Hiramatsu wrote:
> >>> Two high-level comments:
> >>>
> >>>  - There's no self-test - would it be possible to add one? See 
> >>>    trace_selftest* in kernel/trace/
> >> I'm not so sure. Currently, it seems that those self-tests are
> >> only for tracers which define new event-entry on ring-buffer.
> >> Since this tracer just use ftrace_bprintk, it might need
> >> another kind of selftest. e.g. comparing outputs with
> >> expected patterns.
> >> In that case, would it be better to make a user-space self test
> >> including filters and tracepoints?
> > 
> > Or have the workings in the selftest in kernel. As if a user started it. 
> > It does not need to write to the ring buffer, that is just what I did. The 
> > event selftests don't check if anything was written to the ring buffer, 
> > they just make sure that the tests don't crash the system.
> 
> Would you mean that it is enough to enable some probes and just
> see what happened at boot time?
> That's so easy to add.

Yes, that's the idea!

Try to think of regressions/crashes/misbehavior you generally 
trigger while you developed kprobes, and try to add a reasonable set 
of probes that test the code from those angles.

It doesnt have to be a full, complex test-suite, but even just 80% 
of coverage of functionality keeps 4/5th of all regressions out of 
the kernel at a very early stage ...

	Ingo
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