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Message-ID: <4ADAAF50.9040604@redhat.com> Date: Sun, 18 Oct 2009 02:01:52 -0400 From: Masami Hiramatsu <mhiramat@...hat.com> To: Ingo Molnar <mingo@...e.hu> CC: Frederic Weisbecker <fweisbec@...il.com>, Steven Rostedt <rostedt@...dmis.org>, lkml <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, Arnaldo Carvalho de Melo <acme@...hat.com>, Mike Galbraith <efault@....de>, Paul Mackerras <paulus@...ba.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Christoph Hellwig <hch@...radead.org>, Ananth N Mavinakayanahalli <ananth@...ibm.com>, Jim Keniston <jkenisto@...ibm.com>, "Frank Ch. Eigler" <fche@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, systemtap <systemtap@...rces.redhat.com>, DLE <dle-develop@...ts.sourceforge.net> Subject: Re: [PATCH -tip tracing/kprobes 0/9] tracing/kprobes, perf: perf probe and kprobe-tracer bugfixes Ingo Molnar wrote: > > I took a good look at the current bits, and there are a few more things > that need to be fixed before we can consider 'perf probe' for upstream. > > Firstly, this decoder bug is still not fixed: > > CHK include/linux/compile.h > TEST posttest > Error: ffffffff81068fe0: 66 0f 73 fd 04 pslldq $0x4,%xmm5 > Error: objdump says 5 bytes, but insn_get_length() says 4 (attr:8000) > make[1]: *** [posttest] Error 2 > > 64-bit allyesconfig will trigger this for example, but the attached > smaller config too. This needs to be fixed before we can apply any > new commits. Absolutely, yes. Thank you for reporting. I'm checking it again. > Secondly, the probe syntax is quite non-obvious currently. All the 'p' > and -P gymnastics is just a barrier to the first-time user getting his > first probe inserted successfully. Hmm... > The user need not worry about whether it's a 'kprobe' or a 'kretprobe'. > The user should _specify_ what it wants to probe, and _that_ will lead > to 'perf probe' picking the most suitable facility to achieve that kind > of probing. > > It might be a kprobe, a kretprobe, or an mcount driven function probe, > an existing tracepoint if it happens to be present in that place already > - or some other future mechanism. The driving force must be a robust > specification of 'what', not the mechanics of 'how'. Agreed. > Considering that, the current 'perf probe' syntax does not achieve that > goal yet. > > Here are a few syntax suggestions > > The simpest probe syntax should be to add a probe to a single function > name: > > perf probe +schedule > > _nothing else_. > > To remove it, the user should just do something like: > > perf probe -schedule > > (to be symmetric 'perf probe +schedule' should work as well) I think '-<symbol>' syntax doesn't work good with other command-line options and multiple definitions. (However, it will be good for input-from-file syntax. :-)) So, what would you think about using -D (def) and -U (undef) ? > perf probe will make up a synthetic probe name for that - probe-1 for > example. It will also pick the suitable probe mechanism (kprobes). How about [perfprobe:symbol_offs] ? > All the other extensions and possibilities - arguments, variables, > source code lines, etc. should be natural and intuitive extensions of > this basic, minimal syntax. Don't you like current space(' ') separated arguments? :-) I mean, what is 'natural' syntax in your opinion? > > To insert a simple probe no -P should be needed, 'p', no ':' - no probe > name even. Yeah, return-probe and event-name should be optional. > Furthermore, there should be a way to list existing probes (and only > probes), probably via 'perf list --probes' or 'perf probe --list'. OK. I think perf probe --list will list up all probes including user-defined ftrace-event via debugfs (not perf-probe), since perf can use and delete it. > Plus, 'perf probe --help' should list a few simple examples, beyond the > syntax. > > Ok? Sure. Thank you! -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@...hat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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