Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752991AbaKJNy0 (ORCPT ); Mon, 10 Nov 2014 08:54:26 -0500 Received: from mail.kernel.org ([198.145.19.201]:53779 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752917AbaKJNyP (ORCPT ); Mon, 10 Nov 2014 08:54:15 -0500 Date: Mon, 10 Nov 2014 10:54:09 -0300 From: Arnaldo Carvalho de Melo To: Ingo Molnar Cc: Peter Zijlstra , Vince Weaver , Stephane Eranian , Jiri Olsa , Andy Lutomirski , Thomas Gleixner , LKML Subject: Re: [RFD] perf syscall error handling Message-ID: <20141110135409.GR18464@kernel.org> References: <20141031092713.GA23124@gmail.com> <20141031122824.GZ12020@console-pimps.org> <20141103162548.GB18464@kernel.org> <20141103165019.GY10501@worktop.programming.kicks-ass.net> <20141103170059.GC18464@kernel.org> <20141110102725.GA19309@gmail.com> <20141110121527.GQ18464@kernel.org> <20141110122446.GA21503@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141110122446.GA21503@gmail.com> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Mon, Nov 10, 2014 at 01:24:47PM +0100, Ingo Molnar escreveu: > * Arnaldo Carvalho de Melo wrote: > > Em Mon, Nov 10, 2014 at 11:27:25AM +0100, Ingo Molnar escreveu: > > > * Arnaldo Carvalho de Melo wrote: > > > > Em Mon, Nov 03, 2014 at 05:50:19PM +0100, Peter Zijlstra escreveu: > > > > > OK, so how about we do both, the offset+mask for the tools > > > > > and the string for the humans? It looks like machines don't have problems with strings 8-) > > > > Yeah, tooling tries to provide the best it can with the > > > > offset+mask, and if doesn't manage to do anything smart with > > > > it, just show the string and hope that helps the user to figure > > > > out what is happening. > > > Almost: tooling should generally always consider the string as > > > well, for the (not so uncommon) case where there can be multiple > > > problems with the same field. > > > Really, I think the string will give the most bang for the buck, > > > because it's really simple and straightforward on the kernel side > > > (so that we have a good chance of achieving full coverage > > > relatively quickly), and later on we could still complicate it > > > all with offset+mask if there's really a need. > > > So lets start with an error string... > > I don't have a problem with the order of introduction of new > > error reporting mechanisms, or at least I can't think of one > > right now. > > So if we introduce strings now then tools/perf/ will trow them > > to the user when it still don't have fallbacks or any other UI > > indication of such an error. > > I wonder tho if we have any previous experience on some other > > project (or even in the kernel?) and how userspace ended up > > using it, if just presenting those strings to the user or if > > trying to parse it, etc, anybody? > I'm not aware of any such efforts in the Linux space - subsystems > with administrative interfaces generally just tend to printk() a > reason - that's obviously suboptimal in several ways. > Programmatic use in user-spaec is very simple - go with my > initial example, tooling can either just display the error string > and bail out, or do: > if (unlikely(error)) { > if (!strcmp(attr->error_str, "x86/bts: BTS not supported by this CPU architecture")) { > fprintf(stderr, "x86/BTS: No hardware support falling back to branch sampling\n"); > activate_x86_bts_fallback_code(); > goto out; > } > if (!strcmp(attr->error_str, "x86/lbr: LBR not supported by this CPU architecture")) > goto out_err; > } > or it may do any number of other things, such as convert it to > its internal error code. Note that the error messages should have > some minimal structure (the 'x86/bts:' and 'x86/lbr' prefixes) to > organize things nicely and to make string clashes less likely. Right, focus on the string format: Can we just have this two level thing, first part separated by a slash, followed by colon, to identify the origin of the message, and then a message, that can have further, unspecified at this time, parser tokens as the need arises? > as this is a slowpath the performance of strcmp() doesn't matter, > and in any case it's hardware accelerated or optimized well on > most platforms. - Arnaldo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/