From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 14FF8C282DD for ; Fri, 24 May 2019 02:40:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D07A0217D9 for ; Fri, 24 May 2019 02:40:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387669AbfEXCkM (ORCPT ); Thu, 23 May 2019 22:40:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:60978 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727037AbfEXCkM (ORCPT ); Thu, 23 May 2019 22:40:12 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1263F2177E; Fri, 24 May 2019 02:40:09 +0000 (UTC) Date: Thu, 23 May 2019 22:40:08 -0400 From: Steven Rostedt To: Alexei Starovoitov Cc: Kris Van Hees , 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 , Al Viro Subject: Re: [RFC PATCH 00/11] bpf, trace, dtrace: DTrace BPF program type implementation and sample use Message-ID: <20190523224008.55f6d3ab@oasis.local.home> In-Reply-To: <20190524020849.vxg3hqjtnhnicyzp@ast-mbp.dhcp.thefacebook.com> References: <20190521173618.2ebe8c1f@gandalf.local.home> <20190521214325.rr7emn5z3b7wqiiy@ast-mbp.dhcp.thefacebook.com> <20190521174757.74ec8937@gandalf.local.home> <20190522052327.GN2422@oracle.com> <20190522205329.uu26oq2saj56og5m@ast-mbp.dhcp.thefacebook.com> <20190523054610.GR2422@oracle.com> <20190523211330.hng74yi75ixmcznc@ast-mbp.dhcp.thefacebook.com> <20190523190243.54221053@gandalf.local.home> <20190524003148.pk7qbxn7ysievhym@ast-mbp.dhcp.thefacebook.com> <20190523215737.6601ab7c@oasis.local.home> <20190524020849.vxg3hqjtnhnicyzp@ast-mbp.dhcp.thefacebook.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org [ Added Linus and Al ] On Thu, 23 May 2019 19:08:51 -0700 Alexei Starovoitov 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