From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shuyu Wei Subject: Re: [PATCH] ethernet:arc: Fix racing of TX ring buffer Date: Sun, 15 May 2016 20:38:29 +0800 Message-ID: <20160515123829.GA2831@debian-dorm> References: <20160514161602.GA3347@debian-dorm> <20160514200356.GA14105@electric-eye.fr.zoreil.com> <20160514231044.GA2968@debian-dorm> <20160515091953.GA19983@electric-eye.fr.zoreil.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20160515091953.GA19983-lmTtMILVy1jWQcoT9B9Ug5SCg42XY1Uw0E9HWUfgJXw@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-rockchip" Errors-To: linux-rockchip-bounces+glpar-linux-rockchip=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Francois Romieu Cc: linux-rockchip-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, heiko-4mtYJXux2i+zQB+pC5nmwQ@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, wxt-TNX95d0MmH7DzftRWevZcw@public.gmane.org List-Id: linux-rockchip.vger.kernel.org On Sun, May 15, 2016 at 11:19:53AM +0200, Francois Romieu wrote: > > static void arc_emac_tx_clean(struct net_device *ndev) > { > [...] > for (i = 0; i < TX_BD_NUM; i++) { > unsigned int *txbd_dirty = &priv->txbd_dirty; > struct arc_emac_bd *txbd = &priv->txbd[*txbd_dirty]; > struct buffer_state *tx_buff = &priv->tx_buff[*txbd_dirty]; > struct sk_buff *skb = tx_buff->skb; > unsigned int info = le32_to_cpu(txbd->info); > > if ((info & FOR_EMAC) || !txbd->data || !skb) > break; > ^^^^^ > > -> the "break" statement prevents reading all txbds. At most one extra > descriptor is read and this driver isn't in the Mpps business. > You are right, I forgot the break statement. > > I tried your advice, Tx throughput can only reach 5.52MB/s. > > Even with the original code above ? Yes, I left tx_clean unmodified, and took your advice below. I tested it again just now, this time throughput do reach 9.8MB/s, Maybe last time cpu is not idle. I still have a question, is it possible that tx_clean() run between priv->tx_buff[*txbd_curr].skb = skb and dma_wmb()? --- a/drivers/net/ethernet/arc/emac_main.c +++ b/drivers/net/ethernet/arc/emac_main.c @@ -685,13 +685,15 @@ static int arc_emac_tx(struct sk_buff *skb, struct net_device *ndev) wmb(); skb_tx_timestamp(skb); + priv->tx_buff[*txbd_curr].skb = skb; + + dma_wmb(); *info = cpu_to_le32(FOR_EMAC | FIRST_OR_LAST_MASK | len); /* Make sure info word is set */ wmb(); - priv->tx_buff[*txbd_curr].skb = skb; /* Increment index to point to the next BD */ *txbd_curr = (*txbd_curr + 1) % TX_BD_NUM;