netdev - Re: Netperf UDP issue with connected sockets

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Date:   Thu, 17 Nov 2016 10:51:23 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Rick Jones <rick.jones2@....com>, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: Netperf UDP issue with connected sockets

On Thu, 2016-11-17 at 19:30 +0100, Jesper Dangaard Brouer wrote:

> The point is I can see a socket Send-Q forming, thus we do know the
> application have something to send. Thus, and possibility for
> non-opportunistic bulking. Allowing/implementing bulk enqueue from
> socket layer into qdisc layer, should be fairly simple (and rest of
> xmit_more is already in place).  


As I said, you are fooled by TX completions.

Please make sure to increase the sndbuf limits !

echo 2129920 >/proc/sys/net/core/wmem_default

lpaa23:~# sar -n DEV 1 10|grep eth1
10:49:25         eth1      7.00 9273283.00      0.61 2187214.90      0.00      0.00      0.00
10:49:26         eth1      1.00 9230795.00      0.06 2176787.57      0.00      0.00      1.00
10:49:27         eth1      2.00 9247906.00      0.17 2180915.45      0.00      0.00      0.00
10:49:28         eth1      3.00 9246542.00      0.23 2180790.38      0.00      0.00      1.00
10:49:29         eth1      1.00 9239218.00      0.06 2179044.83      0.00      0.00      0.00
10:49:30         eth1      3.00 9248775.00      0.23 2181257.84      0.00      0.00      1.00
10:49:31         eth1      4.00 9225471.00      0.65 2175772.75      0.00      0.00      0.00
10:49:32         eth1      2.00 9253536.00      0.33 2182666.44      0.00      0.00      1.00
10:49:33         eth1      1.00 9265900.00      0.06 2185598.40      0.00      0.00      0.00
10:49:34         eth1      1.00 6949031.00      0.06 1638889.63      0.00      0.00      1.00
Average:         eth1      2.50 9018045.70      0.25 2126893.82      0.00      0.00      0.50


lpaa23:~# ethtool -S eth1|grep more; sleep 1;ethtool -S eth1|grep more
     xmit_more: 2251366909
     xmit_more: 2256011392

lpaa23:~# echo 2256011392-2251366909 | bc
4644483

   PerfTop:   76969 irqs/sec  kernel:96.6%  exact: 100.0% [4000Hz cycles:pp],  (all, 48 CPUs)
---------------------------------------------------------------------------------------------------------------------------------------------------------------

    11.64%  [kernel]  [k] skb_set_owner_w               
     6.21%  [kernel]  [k] queued_spin_lock_slowpath     
     4.76%  [kernel]  [k] _raw_spin_lock                
     4.40%  [kernel]  [k] __ip_make_skb                 
     3.10%  [kernel]  [k] sock_wfree                    
     2.87%  [kernel]  [k] ipt_do_table                  
     2.76%  [kernel]  [k] fq_dequeue                    
     2.71%  [kernel]  [k] mlx4_en_xmit                  
     2.50%  [kernel]  [k] __dev_queue_xmit              
     2.29%  [kernel]  [k] __ip_append_data.isra.40      
     2.28%  [kernel]  [k] udp_sendmsg                   
     2.01%  [kernel]  [k] __alloc_skb                   
     1.90%  [kernel]  [k] napi_consume_skb              
     1.63%  [kernel]  [k] udp_send_skb                  
     1.62%  [kernel]  [k] skb_release_data              
     1.62%  [kernel]  [k] entry_SYSCALL_64_fastpath     
     1.56%  [kernel]  [k] dev_hard_start_xmit           
     1.55%  udpsnd    [.] __libc_send                   
     1.48%  [kernel]  [k] netif_skb_features            
     1.42%  [kernel]  [k] __qdisc_run                   
     1.35%  [kernel]  [k] sk_dst_check                  
     1.33%  [kernel]  [k] sock_def_write_space          
     1.30%  [kernel]  [k] kmem_cache_alloc_node_trace   
     1.29%  [kernel]  [k] __local_bh_enable_ip          
     1.21%  [kernel]  [k] copy_user_enhanced_fast_string
     1.08%  [kernel]  [k] __kmalloc_reserve.isra.40     
     1.08%  [kernel]  [k] SYSC_sendto                   
     1.07%  [kernel]  [k] kmem_cache_alloc_node         
     0.95%  [kernel]  [k] ip_finish_output2             
     0.95%  [kernel]  [k] ktime_get                     
     0.91%  [kernel]  [k] validate_xmit_skb             
     0.88%  [kernel]  [k] sock_alloc_send_pskb          
     0.82%  [kernel]  [k] sock_sendmsg