netdev - Re: [RFC] rps: shortcut net_rps

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Message-ID: <1271683627.3845.44.camel@edumazet-laptop>
Date:	Mon, 19 Apr 2010 15:27:07 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] rps: shortcut net_rps_action()

Le lundi 19 avril 2010 à 20:28 +0800, Changli Gao a écrit :
> On Mon, Apr 19, 2010 at 8:14 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> > As several packets can be enqueued for a given cpu, we would need to
> > keep bitmasks.
> > We would have to add one test in enqueue_to_backlog()
> >
> > if (cpu_test_and_set(cpu, mask)) {
> >        __raise_softirq_irqoff(NET_RX_SOFTIRQ);
> >        array[nb++] = cpu;
> > }
> 
>         rps_lock(queue);
>         if (queue->input_pkt_queue.qlen <= netdev_max_backlog) {
>                 if (queue->input_pkt_queue.qlen) {
> ...
>                 if (napi_schedule_prep(&queue->backlog)) {
> #ifdef CONFIG_RPS
>                         if (cpu != smp_processor_id()) {
>                                 struct rps_remote_softirq_cpus *rcpus =
>                                     &__get_cpu_var(rps_remote_softirq_cpus);
> 
>                                 cpu_set(cpu, rcpus->mask[rcpus->select]);
>                                 __raise_softirq_irqoff(NET_RX_SOFTIRQ);
>                                 goto enqueue;
>                         }
> #endif
>                         __napi_schedule(&queue->backlog);
>                 }
> 
> Only the first packet of a softnet.input_pkt_queue may trigger IPI, so
> we don't need to keep bitmasks.
> 

This is not true Changli

Please read again all previous mails about RPS, or the code.



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