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Date: Thu, 06 Nov 2008 00:14:16 +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 : > Convert loopback device from using common network queues to a per-cpu > receive queue with NAPI. This gives a small 1% performance gain when > measured over 5 runs of tbench. Not sure if it's worth bothering > though. > > Signed-off-by: Stephen Hemminger <shemminger@...tta.com> > > > --- a/drivers/net/loopback.c 2008-11-04 15:36:29.000000000 -0800 > +++ b/drivers/net/loopback.c 2008-11-05 10:00:20.000000000 -0800 > @@ -59,7 +59,10 @@ > > +/* Special case version of napi_schedule since loopback device has no hard irq */ > +void napi_schedule_irq(struct napi_struct *n) > +{ > + if (napi_schedule_prep(n)) { > + list_add_tail(&n->poll_list, &__get_cpu_var(softnet_data).poll_list); > + __raise_softirq_irqoff(NET_RX_SOFTIRQ); > + } > +} > + Stephen, I dont get it. Sure loopback device cannot generate hard irqs, but what prevent's a real hardware interrupt to call NIC driver that can call napi_schedule() and corrupt softnet_data.poll_list ? Why not using a queue dedicated on loopback directly in cpu_var(softnet_data) ? (ie not using a napi structure for each cpu and each loopback dev) This queue would be irq safe yes. net_rx_action could handle this list without local_irq_disable()/local_irq_enable() games. Hum, maybe complex for loopback_dev_stop() to purge all queues without interfering with other namespaces. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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