netdev - Re: 100% CPU load when generating traffic to destination network that nexthop is not reachable

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Date:   Tue, 15 Aug 2017 22:53:05 +0200
From:   Paweł Staszewski <pstaszewski@...are.pl>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: 100% CPU load when generating traffic to destination network that
 nexthop is not reachable

Hi


Patch applied but no change still 100% CPU

perf below:

      1.99%     0.00%  ksoftirqd/1      [kernel.vmlinux] [k] run_ksoftirqd
             |
             ---run_ksoftirqd
                |
                 --1.99%--__softirqentry_text_start
                           |
                            --1.99%--net_rx_action
                                      |
                                       --1.98%--mlx5e_napi_poll
                                                 |
--1.98%--mlx5e_poll_rx_cq
                                                            |
--1.98%--mlx5e_handle_rx_cqe
                                                                       |
--1.96%--napi_gro_receive
|
--1.96%--netif_receive_skb_internal
|
--1.96%--__netif_receive_skb
|
--1.96%--__netif_receive_skb_core
|
--1.95%--ip_rcv
|
--1.95%--ip_rcv_finish
|
--1.94%--ip_forward
|
--1.94%--ip_forward_finish
|
--1.94%--ip_output
|
--1.94%--ip_finish_output
|
--1.94%--ip_finish_output2
|
--1.90%--neigh_resolve_output
|
--1.90%--neigh_event_send
|
--1.90%--__neigh_event_send
|
--1.87%--_raw_write_lock_bh
queued_write_lock
queued_write_lock_slowpath
|
--1.84%--queued_spin_lock_slowpath


W dniu 2017-08-15 o 21:11, Eric Dumazet pisze:
> On Tue, 2017-08-15 at 19:42 +0200, Paweł Staszewski wrote:
>> # To display the perf.data header info, please use
>> --header/--header-only options.
>> #
>> #
>> # Total Lost Samples: 0
>> #
>> # Samples: 2M of event 'cycles'
>> # Event count (approx.): 1585571545969
>> #
>> # Children      Self  Command         Shared Object         Symbol
>> # ........  ........  ..............  ....................
>> ..............................................
>> #
>>        1.82%     0.00%  ksoftirqd/43    [kernel.vmlinux]      [k]
>> __softirqentry_text_start
>>               |
>>                --1.82%--__softirqentry_text_start
>>                          |
>>                           --1.82%--net_rx_action
>>                                     |
>>                                      --1.82%--mlx5e_napi_poll
>>                                                |
>> --1.81%--mlx5e_poll_rx_cq
>>                                                           |
>> --1.81%--mlx5e_handle_rx_cqe
>>                                                                      |
>> --1.79%--napi_gro_receive
>> |
>> --1.78%--netif_receive_skb_internal
>> |
>> --1.78%--__netif_receive_skb
>> |
>> --1.78%--__netif_receive_skb_core
>> |
>> --1.78%--ip_rcv
>> |
>> --1.78%--ip_rcv_finish
>> |
>> --1.76%--ip_forward
>> |
>> --1.76%--ip_forward_finish
>> |
>> --1.76%--ip_output
>> |
>> --1.76%--ip_finish_output
>> |
>> --1.76%--ip_finish_output2
>> |
>> --1.73%--neigh_resolve_output
>> |
>> --1.73%--neigh_event_send
>> |
>> --1.73%--__neigh_event_send
>> |
>> --1.70%--_raw_write_lock_bh
>> queued_write_lock
>> queued_write_lock_slowpath
>> |
>> --1.67%--queued_spin_lock_slowpath
>>
>>
> Please try this :
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 16a1a4c4eb57fa1147f230916e2e62e18ef89562..95e0d7702029b583de8229e3c3eb923f6395b072 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -991,14 +991,18 @@ static void neigh_timer_handler(unsigned long arg)
>   
>   int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
>   {
> -	int rc;
>   	bool immediate_probe = false;
> +	int rc;
> +
> +	/* We _should_ test this under write_lock_bh(&neigh->lock),
> +	 * but this is too costly.
> +	 */
> +	if (READ_ONCE(neigh->nud_state) & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))
> +		return 0;
>   
>   	write_lock_bh(&neigh->lock);
>   
>   	rc = 0;
> -	if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))
> -		goto out_unlock_bh;
>   	if (neigh->dead)
>   		goto out_dead;
>   
>
>
>