Eric Dumazet <edumazet@xxxxxxxxxx> writes: > On Wed, Feb 2, 2022 at 4:28 AM Sebastian Andrzej Siewior > <bigeasy@xxxxxxxxxxxxx> wrote: >> >> Dave suggested a while ago (eleven years by now) "Let's make netif_rx() >> work in all contexts and get rid of netif_rx_ni()". Eric agreed and >> pointed out that modern devices should use netif_receive_skb() to avoid >> the overhead. >> In the meantime someone added another variant, netif_rx_any_context(), >> which behaves as suggested. >> >> netif_rx() must be invoked with disabled bottom halves to ensure that >> pending softirqs, which were raised within the function, are handled. >> netif_rx_ni() can be invoked only from process context (bottom halves >> must be enabled) because the function handles pending softirqs without >> checking if bottom halves were disabled or not. >> netif_rx_any_context() invokes on the former functions by checking >> in_interrupts(). >> >> netif_rx() could be taught to handle both cases (disabled and enabled >> bottom halves) by simply disabling bottom halves while invoking >> netif_rx_internal(). The local_bh_enable() invocation will then invoke >> pending softirqs only if the BH-disable counter drops to zero. >> >> Add a local_bh_disable() section in netif_rx() to ensure softirqs are >> handled if needed. Make netif_rx_ni() and netif_rx_any_context() invoke >> netif_rx() so they can be removed once they are no more users left. >> >> Link: https://lkml.kernel.org/r/20100415.020246.218622820.davem@xxxxxxxxxxxxx >> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > > Maybe worth mentioning this commit will show a negative impact, for > network traffic > over loopback interface. > > My measure of the cost of local_bh_disable()/local_bh_enable() is ~6 > nsec on one of my lab x86 hosts. > > Perhaps we could have a generic netif_rx(), and a __netif_rx() for the > virtual drivers (lo and maybe tunnels). > > void __netif_rx(struct sk_buff *skb); > > static inline int netif_rx(struct sk_buff *skb) > { > int res; > local_bh_disable(); > res = __netif_rx(skb); > local_bh_enable(); > return res; > } +1, this seems like a reasonable solution! -Toke
