From patchwork Thu Feb 26 20:35:05 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ben Hutchings X-Patchwork-Id: 444058 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 2BFEB14012A for ; Fri, 27 Feb 2015 07:35:19 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754536AbbBZUfM (ORCPT ); Thu, 26 Feb 2015 15:35:12 -0500 Received: from ducie-dc1.codethink.co.uk ([185.25.241.215]:46891 "EHLO ducie-dc1.codethink.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753976AbbBZUfK (ORCPT ); Thu, 26 Feb 2015 15:35:10 -0500 Received: from localhost (localhost [127.0.0.1]) by ducie-dc1.codethink.co.uk (Postfix) with ESMTP id 88665460683; Thu, 26 Feb 2015 20:35:09 +0000 (GMT) X-Virus-Scanned: Debian amavisd-new at ducie-dc1.codethink.co.uk Received: from ducie-dc1.codethink.co.uk ([127.0.0.1]) by localhost (ducie-dc1.codethink.co.uk [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Y1+dEP4RBbJO; Thu, 26 Feb 2015 20:35:07 +0000 (GMT) Received: from [192.168.25.61] (unknown [192.168.25.61]) by ducie-dc1.codethink.co.uk (Postfix) with ESMTPSA id 9228D46090E; Thu, 26 Feb 2015 20:35:06 +0000 (GMT) Message-ID: <1424982905.4444.76.camel@xylophone.i.decadent.org.uk> Subject: [PATCH net-next 5/5] sh_eth: Mitigate lost statistics updates From: Ben Hutchings To: netdev@vger.kernel.org Cc: linux-kernel@lists.codethink.co.uk, Nobuhiro Iwamatsu , Mitsuhiro Kimura , Yoshihiro Kaneko , Yoshihiro Shimoda Date: Thu, 26 Feb 2015 20:35:05 +0000 In-Reply-To: <1424982665.4444.70.camel@xylophone.i.decadent.org.uk> References: <1424982665.4444.70.camel@xylophone.i.decadent.org.uk> Organization: Codethink Ltd. X-Mailer: Evolution 3.4.4-3 Mime-Version: 1.0 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The statistics registers have write-clear behaviour, which means we will lose any increment between the read and write. Mitigate this by only clearing when we read a non-zero value, so we will never falsely report a total of zero. This also saves time as we only handle error statistics here and they won't often be incremented. Signed-off-by: Ben Hutchings --- drivers/net/ethernet/renesas/sh_eth.c | 37 ++++++++++++++++++++++----------- 1 file changed, 25 insertions(+), 12 deletions(-) diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c index 38b9d87b2667..c3bc01ccad3e 100644 --- a/drivers/net/ethernet/renesas/sh_eth.c +++ b/drivers/net/ethernet/renesas/sh_eth.c @@ -2414,6 +2414,22 @@ static int sh_eth_start_xmit(struct sk_buff *skb, struct net_device *ndev) return NETDEV_TX_OK; } +/* The statistics registers have write-clear behaviour, which means we + * will lose any increment between the read and write. We mitigate + * this by only clearing when we read a non-zero value, so we will + * never falsely report a total of zero. + */ +static void +sh_eth_update_stat(struct net_device *ndev, unsigned long *stat, int reg) +{ + u32 delta = sh_eth_read(ndev, reg); + + if (delta) { + *stat += delta; + sh_eth_write(ndev, 0, reg); + } +} + static struct net_device_stats *sh_eth_get_stats(struct net_device *ndev) { struct sh_eth_private *mdp = netdev_priv(ndev); @@ -2424,21 +2440,18 @@ static struct net_device_stats *sh_eth_get_stats(struct net_device *ndev) if (!mdp->is_opened) return &ndev->stats; - ndev->stats.tx_dropped += sh_eth_read(ndev, TROCR); - sh_eth_write(ndev, 0, TROCR); /* (write clear) */ - ndev->stats.collisions += sh_eth_read(ndev, CDCR); - sh_eth_write(ndev, 0, CDCR); /* (write clear) */ - ndev->stats.tx_carrier_errors += sh_eth_read(ndev, LCCR); - sh_eth_write(ndev, 0, LCCR); /* (write clear) */ + sh_eth_update_stat(ndev, &ndev->stats.tx_dropped, TROCR); + sh_eth_update_stat(ndev, &ndev->stats.collisions, CDCR); + sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors, LCCR); if (sh_eth_is_gether(mdp)) { - ndev->stats.tx_carrier_errors += sh_eth_read(ndev, CERCR); - sh_eth_write(ndev, 0, CERCR); /* (write clear) */ - ndev->stats.tx_carrier_errors += sh_eth_read(ndev, CEECR); - sh_eth_write(ndev, 0, CEECR); /* (write clear) */ + sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors, + CERCR); + sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors, + CEECR); } else { - ndev->stats.tx_carrier_errors += sh_eth_read(ndev, CNDCR); - sh_eth_write(ndev, 0, CNDCR); /* (write clear) */ + sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors, + CNDCR); } return &ndev->stats;