From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: RPS will assign different smp_processor_id for the same packet?
Date: Sun, 24 Apr 2011 12:53:36 +0200
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Cc: Tom Herbert <therbert@google.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>
To: zhou rui <zhourui.cn@gmail.com>
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Le dimanche 24 avril 2011 =C3=A0 17:36 +0800, zhou rui a =C3=A9crit :
> >
>=20
> my understanding:
>=20
> non-NAPI scenario:
>=20
> netif_rx( in irq, get_rps_cpu,enqueue_to_backlog to deliver packet to
> cpu queue) ------>net_rx_action(in softirq,deque and process packet)
>=20
>=20
> NAPI:
>=20
> what does RPS do?(in
> irq)------------------------>net_rx_action(softirq)----->netif_receiv=
e_skb(get_rps_cpu,enque
> packet)
>=20
> so my question is:
> for NAPI, get_rps_cpu will be done in softirq?
>=20


> if the above situation is true,will this happen?
> packet_for_cpu_1 --> cpu0(netif_receive_skb,in softirq) --->delivered
> to cpu1(softirq)

NAPI is done under softirq, yes.

netif_receive_skb()
	cpu =3D get_rps_cpu()
	if (othercpu(cpu))
		enqueue_to_backlog(cpu)
	else
		__netif_receive_skb(skb);


enqueue_to_backlog() triggers an IPI (hard IRQ) to other cpu1,
to queue an NAPI context. (and triggers softirq)