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Date: Mon, 16 May 2022 13:39:41 -0700 From: Jakub Kicinski <kuba@...nel.org> To: Eric Dumazet <eric.dumazet@...il.com> Cc: "David S . Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, netdev <netdev@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com> Subject: Re: [PATCH net-next 3/4] net: add skb_defer_max sysctl On Sun, 15 May 2022 21:24:55 -0700 Eric Dumazet wrote: > @@ -6494,16 +6495,21 @@ void skb_attempt_defer_free(struct sk_buff *skb) > int cpu = skb->alloc_cpu; > struct softnet_data *sd; > unsigned long flags; > + unsigned int defer_max; > bool kick; > > if (WARN_ON_ONCE(cpu >= nr_cpu_ids) || > !cpu_online(cpu) || > cpu == raw_smp_processor_id()) { > - __kfree_skb(skb); > +nodefer: __kfree_skb(skb); > return; > } > > sd = &per_cpu(softnet_data, cpu); > + defer_max = READ_ONCE(sysctl_skb_defer_max); > + if (READ_ONCE(sd->defer_count) >= defer_max) > + goto nodefer; > + > /* We do not send an IPI or any signal. > * Remote cpu will eventually call skb_defer_free_flush() > */ > @@ -6513,11 +6519,8 @@ void skb_attempt_defer_free(struct sk_buff *skb) > WRITE_ONCE(sd->defer_list, skb); > sd->defer_count++; > > - /* kick every time queue length reaches 128. > - * This condition should hardly be hit under normal conditions, > - * unless cpu suddenly stopped to receive NIC interrupts. > - */ > - kick = sd->defer_count == 128; > + /* Send an IPI every time queue reaches half capacity. */ > + kick = sd->defer_count == (defer_max >> 1); nit: it will behave a little strangely for defer_max == 1 we'll let one skb get onto the list and free the subsequent skbs directly but we'll never kick the IPI Moving the sd->defer_count++; should fix it and have no significant side effects. I think.
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