Commit f52dffe0 authored Nov 23, 2016 by Eric Dumazet Committed by David S. Miller Nov 25, 2016

net: properly flush delay-freed skbs



Typical NAPI drivers use napi_consume_skb(skb) at TX completion time.
This put skb in a percpu special queue, napi_alloc_cache, to get bulk
frees.

It turns out the queue is not flushed and hits the NAPI_SKB_CACHE_SIZE
limit quite often, with skbs that were queued hundreds of usec earlier.
I measured this can take ~6000 nsec to perform one flush.

__kfree_skb_flush() can be called from two points right now :

1) From net_tx_action(), but only for skbs that were queued to
sd->completion_queue.

 -> Irrelevant for NAPI drivers in normal operation.

2) From net_rx_action(), but only under high stress or if RPS/RFS has a
pending action.

This patch changes net_rx_action() to perform the flush in all cases and
after more urgent operations happened (like kicking remote CPUS for
RPS/RFS).

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent ca89fa77

net/core/dev.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -5260,7 +5260,7 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)

		if (list_empty(&list)) {
		if (!sd_has_rps_ipi_waiting(sd) && list_empty(&repoll))
		return;
		goto out;
		break;
		}

		@@ -5278,7 +5278,6 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
		}
		}

		__kfree_skb_flush();
		local_irq_disable();

		list_splice_tail_init(&sd->poll_list, &list);
		@@ -5288,6 +5287,8 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
		__raise_softirq_irqoff(NET_RX_SOFTIRQ);

		net_rps_action_and_irq_enable(sd);
		out:
		__kfree_skb_flush();
		}

		struct netdev_adjacent {