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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D6B59CA0EEB for ; Fri, 30 Aug 2024 07:55:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=JoTkmGymKvepzHlVSjDAM362iJg1UyXTuv5VH8rAMxU=; b=yLa7SLxFp0wRyop0LCvuyuj40R WJRqp/sa5Ma91a6hCalkFsrkexq1wYZ0c0+xRyz1NxfJ3LLX+9Aa8IrN3uNIs5aPfvy/JFB/opxO2 ufV83585o2e5OgeDOSYwpAxs84N+AbcIGyxMoOVkeFW3VE3q0rkiXFSWCn8+OTpDGwhmawCm5/CDL 10RAyab6aQ8MP9QX5VZ3S8zvCcU1HZ34KXfDBz6vQlJsTcqPaKvRHcVGh5WHpFNhI4Q2kEz8gafKt bzNOwGH75S9j6YVbg6TZUzByNtbz1ykShsMRabMQHpph6jUwdHw2CSPChPtsNmBL34pKJCW4H/REp Jop64fyw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sjwTr-00000005CqK-44tF; Fri, 30 Aug 2024 07:55:39 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sjwT0-00000005Ceo-3UF3 for linux-arm-kernel@lists.infradead.org; Fri, 30 Aug 2024 07:54:48 +0000 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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240830_005446_940886_24AA0EFF X-CRM114-Status: GOOD ( 19.66 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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