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Date: Fri, 23 Apr 2010 11:27:05 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Changli Gao <xiaosuo@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, jamal <hadi@...erus.ca>,
Tom Herbert <therbert@...gle.com>,
Stephen Hemminger <shemminger@...tta.com>,
netdev@...r.kernel.org
Subject: Re: [PATCH v6] net: batch skb dequeueing from softnet
input_pkt_queue
Le vendredi 23 avril 2010 à 16:12 +0800, Changli Gao a écrit :
> batch skb dequeueing from softnet input_pkt_queue.
>
> batch skb dequeueing from softnet input_pkt_queue to reduce potential lock
> contention when RPS is enabled.
>
> Note: in the worst case, the number of packets in a softnet_data may be double
> of netdev_max_backlog.
>
> Signed-off-by: Changli Gao <xiaosuo@...il.com>
Very good patch Changli, thanks !
Lets see how it improves thing for Jamal benchs ;)
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ----
> include/linux/netdevice.h | 6 +++--
> net/core/dev.c | 50 +++++++++++++++++++++++++++++++---------------
> 2 files changed, 38 insertions(+), 18 deletions(-)
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 3c5ed5f..6ae9f2b 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1387,6 +1387,7 @@ struct softnet_data {
> struct Qdisc *output_queue;
> struct list_head poll_list;
> struct sk_buff *completion_queue;
> + struct sk_buff_head process_queue;
>
> #ifdef CONFIG_RPS
> struct softnet_data *rps_ipi_list;
> @@ -1401,10 +1402,11 @@ struct softnet_data {
> struct napi_struct backlog;
> };
>
> -static inline void input_queue_head_incr(struct softnet_data *sd)
> +static inline void input_queue_head_add(struct softnet_data *sd,
> + unsigned int len)
> {
> #ifdef CONFIG_RPS
> - sd->input_queue_head++;
> + sd->input_queue_head += len;
> #endif
> }
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a4a7c36..c1585f9 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2409,12 +2409,13 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
> __get_cpu_var(netdev_rx_stat).total++;
>
> rps_lock(sd);
> - if (sd->input_pkt_queue.qlen <= netdev_max_backlog) {
> - if (sd->input_pkt_queue.qlen) {
> + if (skb_queue_len(&sd->input_pkt_queue) <= netdev_max_backlog) {
> + if (skb_queue_len(&sd->input_pkt_queue)) {
> enqueue:
> __skb_queue_tail(&sd->input_pkt_queue, skb);
> #ifdef CONFIG_RPS
> - *qtail = sd->input_queue_head + sd->input_pkt_queue.qlen;
> + *qtail = sd->input_queue_head +
> + skb_queue_len(&sd->input_pkt_queue);
> #endif
> rps_unlock(sd);
> local_irq_restore(flags);
> @@ -2934,13 +2935,21 @@ static void flush_backlog(void *arg)
> struct sk_buff *skb, *tmp;
>
> rps_lock(sd);
> - skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp)
> + skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp) {
> if (skb->dev == dev) {
> __skb_unlink(skb, &sd->input_pkt_queue);
> kfree_skb(skb);
> - input_queue_head_incr(sd);
> + input_queue_head_add(sd, 1);
> }
> + }
> rps_unlock(sd);
> +
> + skb_queue_walk_safe(&sd->process_queue, skb, tmp) {
> + if (skb->dev == dev) {
> + __skb_unlink(skb, &sd->process_queue);
> + kfree_skb(skb);
> + }
> + }
> }
>
> static int napi_gro_complete(struct sk_buff *skb)
> @@ -3286,24 +3295,30 @@ static int process_backlog(struct napi_struct *napi, int quota)
> }
> #endif
> napi->weight = weight_p;
> - do {
> + local_irq_disable();
> + while (1) {
> struct sk_buff *skb;
>
> - local_irq_disable();
> + while ((skb = __skb_dequeue(&sd->process_queue))) {
> + local_irq_enable();
> + __netif_receive_skb(skb);
> + if (++work >= quota)
> + return work;
> + local_irq_disable();
> + }
> +
> rps_lock(sd);
> - skb = __skb_dequeue(&sd->input_pkt_queue);
> - if (!skb) {
> + input_queue_head_add(sd, skb_queue_len(&sd->input_pkt_queue));
> + skb_queue_splice_tail_init(&sd->input_pkt_queue,
> + &sd->process_queue);
> + if (skb_queue_empty(&sd->process_queue)) {
> __napi_complete(napi);
> rps_unlock(sd);
> - local_irq_enable();
> break;
> }
> - input_queue_head_incr(sd);
> rps_unlock(sd);
> - local_irq_enable();
> -
> - __netif_receive_skb(skb);
> - } while (++work < quota);
> + }
> + local_irq_enable();
>
> return work;
> }
> @@ -5631,8 +5646,10 @@ static int dev_cpu_callback(struct notifier_block *nfb,
> /* Process offline CPU's input_pkt_queue */
> while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
> netif_rx(skb);
> - input_queue_head_incr(oldsd);
> + input_queue_head_add(oldsd, 1);
> }
> + while ((skb = __skb_dequeue(&oldsd->process_queue)))
> + netif_rx(skb);
>
> return NOTIFY_OK;
> }
> @@ -5851,6 +5868,7 @@ static int __init net_dev_init(void)
> struct softnet_data *sd = &per_cpu(softnet_data, i);
>
> skb_queue_head_init(&sd->input_pkt_queue);
> + skb_queue_head_init(&sd->process_queue);
> sd->completion_queue = NULL;
> INIT_LIST_HEAD(&sd->poll_list);
>
> --
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