From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: PATCH [0/4] perf: clean-up of power events API Date: Fri, 8 Oct 2010 10:38:19 +0200 Message-ID: <20101008083819.GA22385@elte.hu> References: <1286205661-24448-1-git-send-email-jean.pihet@newoldbits.com> <201010062334.46971.trenn@suse.de> <20101007150825.GB12581@Krystal> <20101007155816.GA5351@nowhere> <4CAED2F0.9080801@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4CAED2F0.9080801@kernel.org> Sender: linux-trace-users-owner@vger.kernel.org To: Tejun Heo Cc: Frederic Weisbecker , Pierre Tardy , Mathieu Desnoyers , Thomas Renninger , Jean Pihet , linux-trace-users@vger.kernel.org, linux-pm@lists.linux-foundation.org, linux-perf-users@vger.kernel.org, arjan@linux.intel.com, rjw@sisk.pl, linux-omap@vger.kernel.org, Peter Zijlstra , Kevin Hilman , Steven Rostedt , Frank Eigler , Masami Hiramatsu , Thomas Gleixner , Andrew Morton , Linus Torvalds List-Id: linux-omap@vger.kernel.org * Tejun Heo wrote: > Hello, > > On 10/07/2010 05:58 PM, Frederic Weisbecker wrote: > > I really feel uncomfortable with this tracepoint/ABI problem.... > > Mathieu suggested we start a user library that could handle these > > changes when they are really necessary. > > > > Thoughts? > > > > (Adding Tejun in Cc). > > Given that tracepoints are supposed to make internal operation > visible. I don't think it's a good idea to make it part of fixed ABI. Yep, exactly. OTOH since it exports information we can do disciplined versioning and extensions only - i.e. leave the old power events around, add the new ones with new distinct names, and phase out the old ones in a kernel cycle or two. It's not hard to do. That way apps can support old kernels too (if they want to), but new events as well - and all in a controlled, non-disruptive manner. More importantly, the kernel wont have cruft and will have no ABI restrictions - the only 'restriction' is to treat information in an append-only manner (i.e. change the event name if you change it materially) - and that's not a big deal here. The fundamental thing about tracing/instrumentation is that there are no deep ABI needs: it's all about analyzing development kernels (and a few select versions that get the enterprise treatment) but otherwise the half-life of this kind of information is very short. So we dont want to tie ourselves down with excessive ABIs. > Maybe some core part can be put in stone but I think things like > internal workqueue implementation should be changeable without > worrying about ABI issues. That's most definitely so! There is and will be zero back-coupling from workqueue tracepoints to workqueue internals. Dont worry about this. Ingo