linux-kernel - Re: [PATCH net-next v7 8/9] xen-netback: Timeout packets in RX path

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Message-ID: <1394707143.25873.30.camel@kazak.uk.xensource.com>
Date:	Thu, 13 Mar 2014 10:39:03 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	<wei.liu2@...rix.com>, <xen-devel@...ts.xenproject.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<jonathan.davies@...rix.com>
Subject: Re: [PATCH net-next v7 8/9] xen-netback: Timeout packets in RX path

On Thu, 2014-03-06 at 21:48 +0000, Zoltan Kiss wrote:
> @@ -557,12 +577,25 @@ void xenvif_disconnect(struct xenvif *vif)
>  void xenvif_free(struct xenvif *vif)
>  {
>  	int i, unmap_timeout = 0;
> +	/* Here we want to avoid timeout messages if an skb can be legitimatly

"legitimately"

> +	 * stucked somewhere else. Realisticly this could be an another vif's

"stuck" and "Realistically"

> +	 * internal or QDisc queue. That another vif also has this
> +	 * rx_drain_timeout_msecs timeout, but the timer only ditches the
> +	 * internal queue. After that, the QDisc queue can put in worst case
> +	 * XEN_NETIF_RX_RING_SIZE / MAX_SKB_FRAGS skbs into that another vif's
> +	 * internal queue, so we need several rounds of such timeouts until we
> +	 * can be sure that no another vif should have skb's from us. We are
> +	 * not sending more skb's, so newly stucked packets are not interesting

"stuck" again.

> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 560950e..bb65c7c 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -63,6 +63,13 @@ module_param(separate_tx_rx_irq, bool, 0644);
>  static unsigned int fatal_skb_slots = FATAL_SKB_SLOTS_DEFAULT;
>  module_param(fatal_skb_slots, uint, 0444);
>  
> +/* When guest ring is filled up, qdisc queues the packets for us, but we have
> + * to timeout them, otherwise other guests' packets can get stucked there

"stuck"

Ian.

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