Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754265AbbFKKZV (ORCPT ); Thu, 11 Jun 2015 06:25:21 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:46894 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752847AbbFKKZQ convert rfc822-to-8bit (ORCPT ); Thu, 11 Jun 2015 06:25:16 -0400 Message-ID: <1434018301.1495.73.camel@twins> Subject: Re: [PATCH 1/2] perf: return ENOENT instead of ENOTSUPP From: Peter Zijlstra To: Hendrik Brueckner Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Vince Weaver , Paul Mackerras , Martin Schwidefsky , Heiko Carstens , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Date: Thu, 11 Jun 2015 12:25:01 +0200 In-Reply-To: <1434016745-17608-1-git-send-email-brueckner@linux.vnet.ibm.com> References: <1434016745-17608-1-git-send-email-brueckner@linux.vnet.ibm.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1207 Lines: 30 On Thu, 2015-06-11 at 11:59 +0200, Hendrik Brueckner wrote: > The ENOTSUPP (which actually should be EOPNOTSUPP for user space) does not > trigger a fallback event selection, for example, by perf record. > If hardware support for the cycles perf event is available, but the hardware > does not provide interrupts, returning ENOTSUPP causes perf to end. Returning > ENOENT causes the perf tool to fallback to a software-based cycle PMU that > supports interrupts. > > The commit 53b25335dd ("perf: Disable sampled events if no PMU interrupt") > introduced that incompatible change. That's 3.16 > if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) { > - err = -ENOTSUPP; > + err = -ENOENT; > goto err_alloc; > } > } And now you would be changing an API that's been around for at least 4 releases. Also, I really think -ENOENT is the wrong return here, you're asking for things that's not supported, not for something that's not there. -- 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/