From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 7D9711531FC; Fri, 30 Aug 2024 07:54:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725004488; cv=none; b=Jkx59oB0HIoH9CC0bONeB85ymnU7eRmpJSWfto6oVWq0XXr12lpGiNAoN1yTCv0mlSnrBM7umU3Tek4A8NDI7epU9P3BvtSAfAHcE1XUyDjoOBJbcqpw1+Ptk45Jw9b7SK9IjONFYXjE0dM5vE1WaoIYcphZ5WISEAmK6zdXfOc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725004488; c=relaxed/simple; bh=ICYHULuCEXJMyFjPlygiTLaIzDP1RtvfBDBMmHAMIlE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SRQctPDMgJSchNkDv1qVT+6dGETEq+wiVC1xFqEIw9nLFmH2EQ+VHmtOdoCu/lEQq2CzqwgDMzLaeRkpxEldamM/WJvkJXpBHwFNPBLHgjgf4E4ml8a1w/qw3e/qbGSiLD3sKB0HKCZTDl02KfRRjxaW2muSVfG9vlwm3IrqAuQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 F11931063; Fri, 30 Aug 2024 00:55:11 -0700 (PDT) Received: from [10.2.76.71] (e132581.arm.com [10.2.76.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C21AD3F73B; Fri, 30 Aug 2024 00:54:43 -0700 (PDT) Message-ID: Date: Fri, 30 Aug 2024 08:54:42 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 9/9] perf arm-spe: Dump metadata with version 2 To: James Clark Cc: Arnaldo Carvalho de Melo , Will Deacon , Mark Rutland , Suzuki K Poulose , Mike Leach , John Garry , Namhyung Kim , Ian Rogers , Adrian Hunter , "Liang, Kan" , Jonathan Cameron , Yicong Yang , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, coresight@lists.linaro.org, linux-perf-users@vger.kernel.org References: <20240827164417.3309560-1-leo.yan@arm.com> <20240827164417.3309560-10-leo.yan@arm.com> Content-Language: en-US From: Leo Yan In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/28/24 17:20, James Clark wrote: >> +static void arm_spe_print_info(struct arm_spe *spe, __u64 *arr) >>   { >> +     unsigned int i, cpu, header_size, cpu_num, per_cpu_size; >> + >>       if (!dump_trace) >>               return; >> >> -     fprintf(stdout, arm_spe_info_fmts[ARM_SPE_PMU_TYPE], arr[ARM_SPE_PMU_TYPE]); >> +     if (spe->metadata_ver == 1) { >> +             cpu_num = 0; >> +             header_size = ARM_SPE_AUXTRACE_V1_PRIV_MAX; >> +             per_cpu_size = 0; >> +     } else if (spe->metadata_ver == 2) { > > Assuming future version updates are backwards compatible and only add > new info this should be spe->metadata_ver >= 2, otherwise version bumps > end up causing errors when files get passed around. > > I know there are arguments about what should and shouldn't be supported > when opening new files on old perfs, but in this case it's easy to only > add new info to the aux header and leave the old stuff intact. > >> +             cpu_num = arr[ARM_SPE_CPU_NUM]; >> +             header_size = ARM_SPE_AUXTRACE_V2_PRIV_MAX; >> +             per_cpu_size = ARM_SPE_AUXTRACE_V2_PRIV_PER_CPU_MAX; > > I think for coresight we also save the size of each per-cpu block rather > than use a constant, that way new items can be appended without breaking > readers. Good point for adding a 'size' field for each per-cpu block. My understanding is we need to make the metadata format to be self-described. E.g. the metadata header contains the size for itself, and every per CPU metadata block also contains a 'size' field. Based on this, a general code can be used to processing different metadata versions. > That kind of leads to another point that this mechanism is mostly > duplicated from coresight. It saves a main header version, then per-cpu > groups of variable size with named elements. I'm not saying we should > definitely try to share the code, but it's worth keeping in mind. Agreed. I will refine a bit, for better matching this direction. Thanks for suggestion. Leo