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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F51EC001DE for ; Thu, 13 Jul 2023 07:31:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234182AbjGMHbH (ORCPT ); Thu, 13 Jul 2023 03:31:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233486AbjGMHbG (ORCPT ); Thu, 13 Jul 2023 03:31:06 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B50D9E77; Thu, 13 Jul 2023 00:31:04 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E4E821570; Thu, 13 Jul 2023 00:31:46 -0700 (PDT) Received: from [10.163.49.144] (unknown [10.163.49.144]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 44FD03F73F; Thu, 13 Jul 2023 00:30:57 -0700 (PDT) Message-ID: Date: Thu, 13 Jul 2023 13:00:55 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH 4/4] perf: Remove unused PERF_PMU_CAP_HETEROGENEOUS_CPUS capability Content-Language: en-US To: James Clark Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Adrian Hunter , Thomas Gleixner , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Will Deacon , Kan Liang , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, irogers@google.com References: <20230710122138.1450930-1-james.clark@arm.com> <20230710122138.1450930-5-james.clark@arm.com> <96a3d12a-71d8-1779-28a3-316e1838292e@arm.com> <6143e1cd-4db7-d980-a189-b9b06f99d7c4@arm.com> From: Anshuman Khandual In-Reply-To: <6143e1cd-4db7-d980-a189-b9b06f99d7c4@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/11/23 19:45, James Clark wrote: > > > On 11/07/2023 13:10, Anshuman Khandual wrote: >> >> >> On 7/10/23 17:51, James Clark wrote: >>> Since commit bd2756811766 ("perf: Rewrite core context handling") the >>> relationship between perf_event_context and PMUs has changed so that >>> the error scenario that PERF_PMU_CAP_HETEROGENEOUS_CPUS originally >>> silenced no longer exists. >>> >>> Remove the capability to avoid confusion that it actually influences >>> any perf core behavior. This change should be a no-op. >>> >>> Signed-off-by: James Clark >>> --- >>> include/linux/perf_event.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h >>> index d5628a7b5eaa..3f4d941fd6c5 100644 >>> --- a/include/linux/perf_event.h >>> +++ b/include/linux/perf_event.h >>> @@ -288,7 +288,7 @@ struct perf_event_pmu_context; >>> #define PERF_PMU_CAP_EXTENDED_REGS 0x0008 >>> #define PERF_PMU_CAP_EXCLUSIVE 0x0010 >>> #define PERF_PMU_CAP_ITRACE 0x0020 >>> -#define PERF_PMU_CAP_HETEROGENEOUS_CPUS 0x0040 >>> +/* Unused 0x0040 */ >> >> Small nit, "Unused" marking might not be required here. >> > > But then it would be very easy to miss that there is a free bit if I > don't leave the comment. Is it really better without it? > > I could shift all the following ones down by one bit, but it would be a Sounds as a better option IMHO. > lot of work to make sure that nobody has hard coded some check for one > of the bits instead of using the define somewhere. These are not user visible ABI and hence defined in include/linux/perf_event.h to be used by drivers registering a PMU for capability enumeration. I am just wondering why they might have been hard coded any where ? > >>> #define PERF_PMU_CAP_NO_EXCLUDE 0x0080 >>> #define PERF_PMU_CAP_AUX_OUTPUT 0x0100 >>> #define PERF_PMU_CAP_EXTENDED_HW_TYPE 0x0200