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Message-ID: <490FED80.9090601@cosmosbay.com>
Date: Tue, 04 Nov 2008 07:36:48 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: Stephen Hemminger <shemminger@...tta.com>
CC: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC] loopback: optimization
Stephen Hemminger a écrit :
> This is something I was trying out to try improving loopback performance.
> It moves loopback processing from the generic backlog per-cpu queues,
> to its own set of queues. I thought this might help the cache locality
> and the loopback doesn't have to do relatively expensive local_irq_disable()
> operations.
>
> BUT it didn't seem to help with tbench, but it might help others who
> want to go farther with it. Code runs but treat it ASIS at this point.
>
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
>
>
> --- a/drivers/net/loopback.c 2008-11-03 10:13:31.000000000 -0800
> +++ b/drivers/net/loopback.c 2008-11-03 11:05:52.000000000 -0800
> @@ -59,51 +59,79 @@
> #include <linux/percpu.h>
> #include <net/net_namespace.h>
>
> -struct pcpu_lstats {
> +struct loopback_per_cpu {
> + struct sk_buff_head rxq;
> + struct napi_struct napi;
> +
> unsigned long packets;
> unsigned long bytes;
> };
>
> +
> /*
> * The higher levels take care of making this non-reentrant (it's
> * called with bh's disabled).
> */
> static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
> {
> - struct pcpu_lstats *pcpu_lstats, *lb_stats;
> + struct loopback_per_cpu *lo = dev->ml_priv, *pcpu;
>
> skb_orphan(skb);
>
> - skb->protocol = eth_type_trans(skb,dev);
> + skb->protocol = eth_type_trans(skb, dev);
>
> dev->last_rx = jiffies;
>
> /* it's OK to use per_cpu_ptr() because BHs are off */
> - pcpu_lstats = dev->ml_priv;
> - lb_stats = per_cpu_ptr(pcpu_lstats, smp_processor_id());
> - lb_stats->bytes += skb->len;
> - lb_stats->packets++;
> + pcpu = per_cpu_ptr(lo, smp_processor_id());
>
> - netif_rx(skb);
> + if (likely(pcpu->rxq.qlen < netdev_max_backlog)) {
> + if (pcpu->rxq.qlen == 0)
> + __napi_schedule(&lo->napi);
Hum...
Most of the time I suspect we take this __napi_schedule() thing.
So are you sure you use the right one (&lo->napi, not &pcpu->napi) ?
This is the where point we still do a cache line ping-pong.
> +
> + __skb_queue_tail(&pcpu->rxq, skb);
> + pcpu->bytes += skb->len;
> + pcpu->packets++;
> +
> + return NET_XMIT_SUCCESS;
> + } else {
> + dev->stats.rx_dropped++;
> + dev_kfree_skb_any(skb);
> + return NET_XMIT_DROP;
> + }
> +}
>
> - return 0;
> +static int loopback_poll(struct napi_struct *napi, int work_limit)
> +{
> + struct loopback_per_cpu *pcpu
> + = container_of(napi, struct loopback_per_cpu, napi);
> + struct sk_buff *skb;
> + int work_done = 0;
> +
> + while ( (skb = __skb_dequeue(&pcpu->rxq)) ) {
> + netif_receive_skb(skb);
> +
> + if (++work_done >= work_limit)
> + goto done;
> + }
> +
> + __napi_complete(napi);
> +done:
> + return work_done;
> }
>
> static struct net_device_stats *get_stats(struct net_device *dev)
> {
> - const struct pcpu_lstats *pcpu_lstats;
> + const struct loopback_per_cpu *lo = dev->ml_priv;
> struct net_device_stats *stats = &dev->stats;
> unsigned long bytes = 0;
> unsigned long packets = 0;
> int i;
>
> - pcpu_lstats = dev->ml_priv;
> for_each_possible_cpu(i) {
> - const struct pcpu_lstats *lb_stats;
> -
> - lb_stats = per_cpu_ptr(pcpu_lstats, i);
> - bytes += lb_stats->bytes;
> - packets += lb_stats->packets;
> + const struct loopback_per_cpu *pcpu = per_cpu_ptr(lo, i);
> + bytes += pcpu->bytes;
> + packets += pcpu->packets;
> }
> stats->rx_packets = packets;
> stats->tx_packets = packets;
> @@ -127,21 +155,43 @@ static const struct ethtool_ops loopback
>
> static int loopback_dev_init(struct net_device *dev)
> {
> - struct pcpu_lstats *lstats;
> + struct loopback_per_cpu *lo;
> + int i;
>
> - lstats = alloc_percpu(struct pcpu_lstats);
> - if (!lstats)
> + lo = alloc_percpu(struct loopback_per_cpu);
> + if (!lo)
> return -ENOMEM;
>
> - dev->ml_priv = lstats;
> + dev->ml_priv = lo;
> +
> + for_each_possible_cpu(i) {
> + struct loopback_per_cpu *pcpu = per_cpu_ptr(lo, i);
> + skb_queue_head_init(&pcpu->rxq);
> + netif_napi_add(dev, &pcpu->napi, loopback_poll, 64);
> + }
> +
> + return 0;
> +}
> +
> +static int loopback_dev_stop(struct net_device *dev)
> +{
> + struct loopback_per_cpu *lo = dev->ml_priv;
> + int i;
> +
> + for_each_possible_cpu(i) {
> + struct loopback_per_cpu *pcpu = per_cpu_ptr(lo, i);
> +
> + napi_synchronize(&pcpu->napi);
> + __skb_queue_purge(&pcpu->rxq);
> + }
> return 0;
> }
>
> static void loopback_dev_free(struct net_device *dev)
> {
> - struct pcpu_lstats *lstats = dev->ml_priv;
> + struct loopback_per_cpu *lo = dev->ml_priv;
>
> - free_percpu(lstats);
> + free_percpu(lo);
> free_netdev(dev);
> }
>
> @@ -169,6 +219,7 @@ static void loopback_setup(struct net_de
> dev->header_ops = ð_header_ops;
> dev->init = loopback_dev_init;
> dev->destructor = loopback_dev_free;
> + dev->stop = loopback_dev_stop;
> }
>
> --
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>
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