From: Alexei Starovoitov <firstname.lastname@example.org> To: Steven Rostedt <email@example.com> Cc: Kris Van Hees <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [RFC PATCH 00/11] bpf, trace, dtrace: DTrace BPF program type implementation and sample use Date: Thu, 23 May 2019 19:08:51 -0700 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On Thu, May 23, 2019 at 09:57:37PM -0400, Steven Rostedt wrote: > On Thu, 23 May 2019 17:31:50 -0700 > Alexei Starovoitov <firstname.lastname@example.org> wrote: > > > > > Now from what I'm reading, it seams that the Dtrace layer may be > > > abstracting out fields from the kernel. This is actually something I > > > have been thinking about to solve the "tracepoint abi" issue. There's > > > usually basic ideas that happen. An interrupt goes off, there's a > > > handler, etc. We could abstract that out that we trace when an > > > interrupt goes off and the handler happens, and record the vector > > > number, and/or what device it was for. We have tracepoints in the > > > kernel that do this, but they do depend a bit on the implementation. > > > Now, if we could get a layer that abstracts this information away from > > > the implementation, then I think that's a *good* thing. > > > > I don't like this deferred irq idea at all. > > What do you mean deferred? that's how I interpreted your proposal: "interrupt goes off and the handler happens, and record the vector number" It's not a good thing to tell about irq later. Just like saying lets record perf counter event and report it later. > > Abstracting details from the users is _never_ a good idea. > > Really? Most everything we do is to abstract details from the user. The > key is to make the abstraction more meaningful than the raw data. > > > A ton of people use bcc scripts and bpftrace because they want those details. > > They need to know what kernel is doing to make better decisions. > > Delaying irq record is the opposite. > > I never said anything about delaying the record. Just getting the > information that is needed. > > > > > > > I wish that was totally true, but tracepoints *can* be an abi. I had > > > code reverted because powertop required one to be a specific > > > format. To this day, the wakeup event has a "success" field that > > > writes in a hardcoded "1", because there's tools that depend on it, > > > and they only work if there's a success field and the value is 1. > > > > I really think that you should put powertop nightmares to rest. > > That was long ago. The kernel is different now. > > Is it? > > > Linus made it clear several times that it is ok to change _all_ > > tracepoints. Period. Some maintainers somehow still don't believe > > that they can do it. > > From what I remember him saying several times, is that you can change > all tracepoints, but if it breaks a tool that is useful, then that > change will get reverted. He will allow you to go and fix that tool and > bring back the change (which was the solution to powertop). my interpretation is different. We changed tracepoints. It broke scripts. People changed scripts. > > > > > Some tracepoints are used more than others and more people will > > complain: "ohh I need to change my script" when that tracepoint > > changes. But the kernel development is not going to be hampered by a > > tracepoint. No matter how widespread its usage in scripts. > > That's because we'll treat bpf (and Dtrace) scripts like modules (no > abi), at least we better. But if there's a tool that doesn't use the > script and reads the tracepoint directly via perf, then that's a > different story. absolutely not. tracepoint is a tracepoint. It can change regardless of what and how is using it.
next prev parent reply index Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-05-20 23:47 Kris Van Hees 2019-05-21 17:56 ` Alexei Starovoitov 2019-05-21 18:41 ` Kris Van Hees 2019-05-21 20:55 ` Alexei Starovoitov 2019-05-21 21:36 ` Steven Rostedt 2019-05-21 21:43 ` Alexei Starovoitov 2019-05-21 21:48 ` Steven Rostedt 2019-05-22 5:23 ` Kris Van Hees 2019-05-22 20:53 ` Alexei Starovoitov 2019-05-23 5:46 ` Kris Van Hees 2019-05-23 21:13 ` Alexei Starovoitov 2019-05-23 23:02 ` Steven Rostedt 2019-05-24 0:31 ` Alexei Starovoitov 2019-05-24 1:57 ` Steven Rostedt 2019-05-24 2:08 ` Alexei Starovoitov [this message] 2019-05-24 2:40 ` Steven Rostedt 2019-05-24 5:26 ` Kris Van Hees 2019-05-24 5:10 ` Kris Van Hees 2019-05-24 4:05 ` Kris Van Hees 2019-05-24 13:28 ` Steven Rostedt 2019-05-21 21:36 ` Kris Van Hees 2019-05-21 23:26 ` Alexei Starovoitov 2019-05-22 4:12 ` Kris Van Hees 2019-05-22 20:16 ` Alexei Starovoitov 2019-05-23 5:16 ` Kris Van Hees 2019-05-23 20:28 ` Alexei Starovoitov 2019-05-30 16:15 ` Kris Van Hees 2019-05-31 15:25 ` Chris Mason 2019-06-06 20:58 ` Kris Van Hees 2019-06-18 1:25 ` Kris Van Hees 2019-06-18 1:32 ` Alexei Starovoitov 2019-06-18 1:54 ` Kris Van Hees 2019-06-18 3:01 ` Alexei Starovoitov 2019-06-18 3:19 ` Kris Van Hees 2019-05-22 14:25 ` Peter Zijlstra 2019-05-22 18:22 ` Kris Van Hees 2019-05-22 19:55 ` Alexei Starovoitov 2019-05-22 20:20 ` David Miller 2019-05-23 5:19 ` Kris Van Hees 2019-05-24 7:27 ` Peter Zijlstra 2019-05-21 20:39 ` [RFC PATCH 01/11] bpf: context casting for tail call Kris Van Hees 2019-05-21 20:39 ` [RFC PATCH 02/11] bpf: add BPF_PROG_TYPE_DTRACE Kris Van Hees 2019-05-21 20:39 ` [RFC PATCH 03/11] bpf: export proto for bpf_perf_event_output helper Kris Van Hees [not found] ` <facilities> 2019-05-21 20:39 ` [RFC PATCH 04/11] trace: initial implementation of DTrace based on kernel Kris Van Hees 2019-05-21 20:39 ` [RFC PATCH 05/11] trace: update Kconfig and Makefile to include DTrace Kris Van Hees [not found] ` <features> 2019-05-21 20:39 ` [RFC PATCH 06/11] dtrace: tiny userspace tool to exercise DTrace support Kris Van Hees 2019-05-21 20:39 ` [RFC PATCH 07/11] bpf: implement writable buffers in contexts Kris Van Hees 2019-05-21 20:39 ` [RFC PATCH 08/11] perf: add perf_output_begin_forward_in_page Kris Van Hees [not found] ` <the> [not found] ` <context> 2019-05-21 20:39 ` [RFC PATCH 09/11] bpf: mark helpers explicitly whether they may change Kris Van Hees [not found] ` <helpers> 2019-05-21 20:39 ` [RFC PATCH 10/11] bpf: add bpf_buffer_reserve and bpf_buffer_commit Kris Van Hees 2019-05-21 20:40 ` [RFC PATCH 11/11] dtrace: make use of writable buffers in BPF Kris Van Hees 2019-05-21 20:48 ` [RFC PATCH 00/11] bpf, trace, dtrace: DTrace BPF program type implementation and sample use Kris Van Hees 2019-05-21 20:54 ` Steven Rostedt 2019-05-21 20:56 ` Alexei Starovoitov
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