netdev - Re: [PATCH net-next-2.6] net: Xmit Packet Steering (XPS)

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Message-ID: <412e6f7f0911191812uf0abc61w2f0d44f4d71bd55@mail.gmail.com>
Date:	Fri, 20 Nov 2009 10:12:18 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] net: Xmit Packet Steering (XPS)

On Fri, Nov 20, 2009 at 7:46 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 9977288..9e134f6 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2000,6 +2001,7 @@ gso:
>         */
>        rcu_read_lock_bh();
>
> +       skb->sending_cpu = cpu = smp_processor_id();
>        txq = dev_pick_tx(dev, skb);
>        q = rcu_dereference(txq->qdisc);

I think assigning cpu to skb->sending_cpu just before calling
hard_start_xmit is better, because the CPU which dequeues the skb will
be another one.

>
> @@ -2024,8 +2026,6 @@ gso:
>           Either shot noqueue qdisc, it is even simpler 8)
>         */
>        if (dev->flags & IFF_UP) {
> -               int cpu = smp_processor_id(); /* ok because BHs are off */
> -
>                if (txq->xmit_lock_owner != cpu) {
>
>                        HARD_TX_LOCK(dev, txq, cpu);
> @@ -2967,7 +2967,7 @@ static void net_rx_action(struct softirq_action *h)
>        }
>  out:
>        local_irq_enable();
> -
> +       xps_flush();

If there isn't any new skbs, the memory will be hold forever. I know
you want to eliminate unnecessary IPI, how about sending IPI only when
the remote xps_pcpu_queues are changed from empty to nonempty?


-- 
Regards，
Changli Gao(xiaosuo@...il.com)
--
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