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Date: Mon, 16 May 2022 13:43:22 -0700 From: Eric Dumazet <edumazet@...gle.com> To: Jakub Kicinski <kuba@...nel.org> Cc: Eric Dumazet <eric.dumazet@...il.com>, "David S . Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, netdev <netdev@...r.kernel.org> Subject: Re: [PATCH net-next 3/4] net: add skb_defer_max sysctl On Mon, May 16, 2022 at 1:39 PM Jakub Kicinski <kuba@...nel.org> wrote: > > 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 Yes, I was aware of this, but decided it was not a big deal. Presumably people will be interested to disable the thing completely, I am not sure about defer_max == 1 > > Moving the sd->defer_count++; should fix it and have no significant > side effects. I think. SGTM, thanks !
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