From patchwork Mon Jul 3 10:57:43 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tero Kristo X-Patchwork-Id: 13299967 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 3553BEB64DD for ; Mon, 3 Jul 2023 10:58:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229585AbjGCK6j (ORCPT ); Mon, 3 Jul 2023 06:58:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229484AbjGCK6i (ORCPT ); Mon, 3 Jul 2023 06:58:38 -0400 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A1484C9; Mon, 3 Jul 2023 03:58:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1688381917; x=1719917917; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=aDd9Dd7JEfe7wMOXCs64FITvs+m6jxeMPO7Bg5RtL0s=; b=ik0PfakRSTeHCimtnIGzMAlYS5YXdPLfqHeVSgMev13wKwMVVoO3O1tK 8+qYeYyEKvJza6ElXUxjx3viQNiyfIUb8/AAQfmqZsoUogAIq0aF6GPT5 4//c9qae6svL0hoKp9JOMyGuh8IjgNFYoJFpYBz3O+Y/1duc+gkIwJGCW EoqXTgE9F5DDu7Wb4rJN23f/24WQ+iWt5F+nwipL4lhQnNKqSBPOyxOdj ognVbzJPxUlLIG3idGil2Z7EZXa6TICL6ZOiERlrQTSMj1Aw42DH9gcps 2LVLvpdHOsP6GgLsuQhCDOtHziippfOKaBX/iVByAD1hwv5/sV2X54zqd Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10759"; a="360329699" X-IronPort-AV: E=Sophos;i="6.01,178,1684825200"; d="scan'208";a="360329699" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Jul 2023 03:58:27 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10759"; a="748108247" X-IronPort-AV: E=Sophos;i="6.01,178,1684825200"; d="scan'208";a="748108247" Received: from agrabezh-mobl1.ccr.corp.intel.com (HELO tkristo-desk.intel.com) ([10.252.48.27]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Jul 2023 03:58:23 -0700 From: Tero Kristo To: shuah@kernel.org, tglx@linutronix.de, x86@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, mingo@redhat.com Cc: ast@kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, andrii@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org Subject: [PATCH 0/2] x86/BPF: Add new BPF helper call bpf_rdtsc Date: Mon, 3 Jul 2023 13:57:43 +0300 Message-Id: <20230703105745.1314475-1-tero.kristo@linux.intel.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Hello, This patch series adds a new x86 arch specific BPF helper, bpf_rdtsc() which can be used for reading the hardware time stamp counter (TSC.) Currently the same counter is directly accessible from userspace (using RDTSC instruction), and kernel space using various rdtsc_*() APIs, however eBPF lacks the support. The main usage for the TSC counter is for various profiling and timing purposes, getting accurate cycle counter values. The counter can be currently read from BPF programs by using the existing perf subsystem services (bpf_perf_event_read()), however its usage is cumbersome at best. Additionally, the perf subsystem provides relative value only for the counter, but absolute values are desired by some use cases like Wult [1]. The absolute value of TSC can be read with BPF programs currently via some kprobe / bpf_core_read() magic (see [2], [3], [4] for example), but this relies on accessing kernel internals and is not stable API, and is pretty cumbersome. Thus, this patch proposes a new arch x86 specific BPF helper to avoid the above issues. -Tero [1] https://github.com/intel/wult [2] https://github.com/intel/wult/blob/c92237c95b898498faf41e6644983102d1fe5156/helpers/wult-tdt-helper/tdt-bpf.c#L102 [3] https://github.com/intel/wult/blob/c92237c95b898498faf41e6644983102d1fe5156/helpers/wult-tdt-helper/tdt-bpf.c#L133 [4] https://github.com/intel/wult/blob/c92237c95b898498faf41e6644983102d1fe5156/helpers/wult-tdt-helper/tdt-bpf.c#L488 Acked-by: John Fastabend