|From:||Mathieu Desnoyers <mathieu.desnoyers-AT-efficios.com>|
|To:||Ingo Molnar <mingo-AT-elte.hu>|
|Subject:||Re: [PATCH 09/11] sched: export task_prio to GPL modules|
|Date:||Wed, 7 Dec 2011 17:57:58 -0500|
|Cc:||Greg KH <greg-AT-kroah.com>, Peter Zijlstra <peterz-AT-infradead.org>, devel-AT-driverdev.osuosl.org, lttng-dev-AT-lists.lttng.org, linux-kernel-AT-vger.kernel.org, Linus Torvalds <torvalds-AT-linux-foundation.org>, Andrew Morton <akpm-AT-linux-foundation.org>, Thomas Gleixner <tglx-AT-linutronix.de>, Steven Rostedt <rostedt-AT-goodmis.org>, Frederic Weisbecker <fweisbec-AT-gmail.com>|
Hi Ingo, * Ingo Molnar (firstname.lastname@example.org) wrote: [...] > Mathieu, please work with the tracing folks who DO care about > this stuff. It's not like there's a lack of interest in this > area, nor is there a lack of willingness to take patches. What > there is a lack of is your willingness to actually work on > getting something unified, integrated to users... > > LTTNG has been going on for how many years? I havent seen many > steps towards actually *merging* its functionality - you insist > on doing your own random thing, which is different in random > ways. Yes, some of those random ways may in fact be better than > what we have upstream - would you be interested in filtering > those out and pushing them upstream? I certainly would like to > see that happen. > > We want to pick the best features, and throw away current > upstream code in favor of superior out of tree code - this > concept of letting crap sit alongside each other when people do > care i cannot agree with. LTTng 2.0, today, offers a unified interface for kernel and userspace tracing, in the form of libraries and git-alike command line user interface. It produces a trace format (CTF) that has been developed in collaboration with hardware vendors and reviewed by tracing developers of the Linux community, which allows analyzing correlated traces across the software and hardware stacks, and supports being streamed over the network with zero-copy both in TCP, UDP format, with optional encryption, checksum, and more. It supports multiple concurrent users, and hooks with tracepoints, Perf PMU counters, kprobes, kretprobes, and system calls, with the ability to attach "context" information prepended before each event record as selected by the user when setting up a tracing session. It is currently self-contained: it's been designed to be shipped as a stand-alone set of self-contained modules, but I recently received the offer to get it pulled into staging, which I accepted. In my opinion, tracers need to be split into three distinct parts: 1) core tracing infrastructure that _needs to_ be shared. This mainly targets instrumentation, and I've done my share of contribution to mainline on this front already. I think the infrastructure we have today is in pretty good shape. 2) tracing infrastructure that _could_ be shared. I'm mostly targeting ring buffers and trace clocks there. It could be a nice-to-have to share the implementation, as long as it does not get in the way of what each project is trying to achieve. So far, what I noticed is that each project is lacking understanding of the intent and constraints of the other projects, thus either considering what the others are doing as over- or under- engineering, depending on the context. Therefore, as long as there is no agreement on the right amount of care that needs to be put in the design of these components, it might be best to duplicate the implementation and slowly converge as each project gets to understand the other project's constraints. To make progress on this front, you need to have both code-bases into mainline. 3) interfaces to user-space: very much like filesystems, these ABIs don't need to be shared across projects that have different use-cases. Having multiple tracer ABIs, if self-contained, should not hurt anybody and just increase the rate of innovation. Sadly, the ABIs exposed by perf/ftrace do not seem to be a good fit for LTTng use-cases. Since the perf/ftrace ABIs, as well as the LTTng ABI, are all already used by many tools, it will likely be really difficult to change them overnight. As an example of where we could benefit from working together, LTTng is currently using a shadow copy of the TRACE_EVENT macros, because the upstream version is quite limiting with respect to generating compact probe code. It could be good to integrate those changes upstream, and I think the best way to achieve this is if the perf and ftrace developers can have a look at the approach taken by LTTng to achieve this -- which is better done if LTTng is merged into staging. Another example is how LTTng extracts system call arguments types, which is performed by generating TRACE_EVENT description of the system call table with a script. We could definitely help out each other in this area. There are certainly many other areas where we could eventually benefit from working together, listed above as #2 "tracing infrastructure that _could_ be shared", but I think it is better to first focus on the core infrastructure that we need to share before getting into the territory of the infrastructure we could share if took the time to understand each other's requirements fully first. Meanwhile, having a duplicated implementation of these parts that "could" be shared should not hurt anyone -- it would even help understanding each other --, as long as they stay self-contained. In summary, I'm really open to help out on working on common pieces of infrastructures, but for that they need to take into account both the current perf/ftrace use-cases and the LTTng use-cases. Best regards, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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