From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by dpdk.org (Postfix) with ESMTP id 163DD559C for ; Mon, 8 Feb 2016 16:42:30 +0100 (CET) Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga103.fm.intel.com with ESMTP; 08 Feb 2016 07:42:30 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.22,416,1449561600"; d="scan'208";a="742490610" Received: from sie-lab-212-120.ir.intel.com (HELO silpixa00394367.ir.intel.com) ([10.237.212.120]) by orsmga003.jf.intel.com with ESMTP; 08 Feb 2016 07:42:28 -0800 From: Harry van Haaren To: jing.d.chen@intel.com Date: Mon, 8 Feb 2016 15:42:17 +0000 Message-Id: <1454946137-5505-1-git-send-email-harry.van.haaren@intel.com> X-Mailer: git-send-email 2.5.0 Cc: dev@dpdk.org Subject: [dpdk-dev] [PATCH] docs: add statistics read frequency to fm10k guide X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 08 Feb 2016 15:42:31 -0000 This patch documents that the statistics of fm10k based NICs must be read regularly in order to avoid an undetected 32 bit integer-overflow. Signed-off-by: Harry van Haaren --- doc/guides/nics/fm10k.rst | 16 ++++++++++++++++ doc/guides/rel_notes/release_2_3.rst | 4 ++++ 2 files changed, 20 insertions(+) diff --git a/doc/guides/nics/fm10k.rst b/doc/guides/nics/fm10k.rst index 4206b7f..4250c9e 100644 --- a/doc/guides/nics/fm10k.rst +++ b/doc/guides/nics/fm10k.rst @@ -65,3 +65,19 @@ The FM10000 family of NICS support a maximum of a 15K jumbo frame. The value is fixed and cannot be changed. So, even when the ``rxmode.max_rx_pkt_len`` member of ``struct rte_eth_conf`` is set to a value lower than 15364, frames up to 15364 bytes can still reach the host interface. + +Statistic Polling Frequency +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The FM10000 NICs expose a set of statistics via the PCI BARs. These statistics +are read from the hardware registers when ``rte_eth_stats_get()`` or +``rte_eth_xstats_get()`` is called. The packet counting registers are 32 bits +while the byte counting registers are 48 bits. As a result, the statistics must +be polled regularly in order to ensure the consistency of the returned reads. + +Given the PCIe Gen3 x8, about 50Gbps of traffic can occur. With 64 byte packets +this gives almost 100 million packets/second, causing 32 bit integer overflow +after approx 40 seconds. To ensure these overflows are detected and accounted +for in the statistics, it is necessary to read statistic regularly. It is +suggested to read stats every 20 seconds, which will gaurantee the statistics +are accurate. diff --git a/doc/guides/rel_notes/release_2_3.rst b/doc/guides/rel_notes/release_2_3.rst index 99de186..f966940 100644 --- a/doc/guides/rel_notes/release_2_3.rst +++ b/doc/guides/rel_notes/release_2_3.rst @@ -15,6 +15,10 @@ EAL Drivers ~~~~~~~ +* **FM10K: Statistics Polling Frequency** + + A section has been added to the NIC guide for fm10k about the time + between reading statistics and 32 bit packet counter overflows. Libraries ~~~~~~~~~ -- 2.5.0