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Date: Wed, 9 Sep 2015 15:34:16 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: David Vrabel <david.vrabel@...rix.com>
Cc: netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
Wei Liu <wei.liu2@...rix.com>,
Ian Campbell <ian.campbell@...rix.com>
Subject: Re: [Xen-devel] [PATCHv1 net] xen-netback: require fewer guest Rx
slots when not using GSO
On Tue, Sep 08, 2015 at 02:25:14PM +0100, David Vrabel wrote:
> Commit f48da8b14d04ca87ffcffe68829afd45f926ec6a (xen-netback: fix
> unlimited guest Rx internal queue and carrier flapping) introduced a
> regression.
>
> The PV frontend in IPXE only places 4 requests on the guest Rx ring.
in IPXE ? What is that?
Is that MiniOS with PXE built in?
Does it always place 4 requests? For every operation?
> Since netback required at least (MAX_SKB_FRAGS + 1) slots, IPXE could
> not receive any packets.
>
> a) If GSO is not enabled on the VIF, fewer guest Rx slots are required
> for the largest possible packet. Calculate the required slots
s/slots/slot number/
> based on the maximum GSO size or the MTU.
>
> This calculation of the number of required slots relies on
> 1650d5455bd2 (xen-netback: always fully coalesce guest Rx packets)
> which present in 4.0-rc1 and later.
>
> b) Reduce the Rx stall detection to checking for at least one
s/to/by/
> available Rx request. This is fine since we're predominately
> concerned with detecting interfaces which are down and thus have
> zero available Rx requests.
s/have zero available Rx requests/no available Rx requests/?
>
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> ---
> drivers/net/xen-netback/common.h | 10 ----------
> drivers/net/xen-netback/netback.c | 23 ++++++++++++++++-------
> 2 files changed, 16 insertions(+), 17 deletions(-)
>
> Note that this can only be backported as-is on top of
> 1650d5455bd2dc6b5ee134bd6fc1a3236c266b5b (xen-netback: always fully
> coalesce guest Rx packets) which is in 4.0 and later.
>
> diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
> index 8a495b3..25990b1 100644
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -200,11 +200,6 @@ struct xenvif_queue { /* Per-queue data for xenvif */
> struct xenvif_stats stats;
> };
>
> -/* Maximum number of Rx slots a to-guest packet may use, including the
> - * slot needed for GSO meta-data.
> - */
> -#define XEN_NETBK_RX_SLOTS_MAX (MAX_SKB_FRAGS + 1)
> -
> enum state_bit_shift {
> /* This bit marks that the vif is connected */
> VIF_STATUS_CONNECTED,
> @@ -306,11 +301,6 @@ int xenvif_dealloc_kthread(void *data);
>
> void xenvif_rx_queue_tail(struct xenvif_queue *queue, struct sk_buff *skb);
>
> -/* Determine whether the needed number of slots (req) are available,
> - * and set req_event if not.
> - */
> -bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue, int needed);
> -
> void xenvif_carrier_on(struct xenvif *vif);
>
> /* Callback from stack when TX packet can be released */
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 3f44b52..e791930 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -149,9 +149,20 @@ static inline pending_ring_idx_t pending_index(unsigned i)
> return i & (MAX_PENDING_REQS-1);
> }
>
> -bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue, int needed)
> +static int xenvif_rx_ring_slots_needed(struct xenvif *vif)
> +{
> + if (vif->gso_mask)
> + return DIV_ROUND_UP(vif->dev->gso_max_size, PAGE_SIZE) + 1;
> + else
> + return DIV_ROUND_UP(vif->dev->mtu, PAGE_SIZE);
> +}
> +
> +static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
> {
> RING_IDX prod, cons;
> + int needed;
> +
> + needed = xenvif_rx_ring_slots_needed(queue->vif);
>
> do {
> prod = queue->rx.sring->req_prod;
> @@ -513,7 +524,7 @@ static void xenvif_rx_action(struct xenvif_queue *queue)
>
> skb_queue_head_init(&rxq);
>
> - while (xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX)
> + while (xenvif_rx_ring_slots_available(queue)
> && (skb = xenvif_rx_dequeue(queue)) != NULL) {
> queue->last_rx_time = jiffies;
>
> @@ -1839,8 +1850,7 @@ static bool xenvif_rx_queue_stalled(struct xenvif_queue *queue)
> prod = queue->rx.sring->req_prod;
> cons = queue->rx.req_cons;
>
> - return !queue->stalled
> - && prod - cons < XEN_NETBK_RX_SLOTS_MAX
> + return !queue->stalled && prod - cons < 1
> && time_after(jiffies,
> queue->last_rx_time + queue->vif->stall_timeout);
> }
> @@ -1852,14 +1862,13 @@ static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
> prod = queue->rx.sring->req_prod;
> cons = queue->rx.req_cons;
>
> - return queue->stalled
> - && prod - cons >= XEN_NETBK_RX_SLOTS_MAX;
> + return queue->stalled && prod - cons >= 1;
> }
>
> static bool xenvif_have_rx_work(struct xenvif_queue *queue)
> {
> return (!skb_queue_empty(&queue->rx_queue)
> - && xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX))
> + && xenvif_rx_ring_slots_available(queue))
> || (queue->vif->stall_timeout &&
> (xenvif_rx_queue_stalled(queue)
> || xenvif_rx_queue_ready(queue)))
> --
> 2.1.4
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel
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