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From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Kris Van Hees <kris.van.hees@oracle.com>,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	dtrace-devel@oss.oracle.com, linux-kernel@vger.kernel.org,
	mhiramat@kernel.org, acme@kernel.org, ast@kernel.org,
	daniel@iogearbox.net, peterz@infradead.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [RFC PATCH 00/11] bpf, trace, dtrace: DTrace BPF program type implementation and sample use
Date: Thu, 23 May 2019 22:40:08 -0400
Message-ID: <20190523224008.55f6d3ab@oasis.local.home> (raw)
In-Reply-To: <20190524020849.vxg3hqjtnhnicyzp@ast-mbp.dhcp.thefacebook.com>


[ Added Linus and Al ]

On Thu, 23 May 2019 19:08:51 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> > > > 
> > > > 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.

Scripts are different than binary tools.

> 
> >   
> > > 
> > > 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.

Instead of putting words into Linus's mouth, I'll just let him speak
for himself. If a useful tool that reads a tracepoint breaks because we
changed the tracepoint, and Linus is fine with that. Then great, we can
start adding them to VFS and not worry about them being an ABI.

-- Steve



  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
2019-05-24  2:40                             ` Steven Rostedt [this message]
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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