netdev - Re: [PATCH net-next 0/3] v3 GRE: TCP segmentation offload

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Message-ID: <1360975955.19353.32.camel@edumazet-glaptop>
Date:	Fri, 15 Feb 2013 16:52:35 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	pshelar@...ira.com, netdev@...r.kernel.org, edumazet@...gle.com,
	jesse@...ira.com, bhutchings@...arflare.com, mirqus@...il.com
Subject: Re: [PATCH net-next 0/3] v3 GRE: TCP segmentation offload

On Fri, 2013-02-15 at 15:18 -0500, David Miller wrote:

> All applied, incorporating the suggestions/fixes from Eric.  Specifically,
> using skb_reset_mac_len() in patch #2 and computing pkt_len before ip_local_out()
> in patch #3.

Thanks David

There is this "tx-nocache-copy" issue : 

We currently enable the nocache copy for all devices but loopback.

But its a loss of performance with tunnel devices 

Actually, it seems a loss even for regular ethernet devices :(



# ethtool -K gre1 tx-nocache-copy on 
# perf stat netperf -H 7.7.8.84
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 7.7.8.84 () port 0 AF_INET
Recv   Send    Send                          
Socket Socket  Message  Elapsed              
Size   Size    Size     Time     Throughput  
bytes  bytes   bytes    secs.    10^6bits/sec  

 87380  16384  16384    10.00    4252.42   

 Performance counter stats for 'netperf -H 7.7.8.84':

       9967.965824 task-clock                #    0.996 CPUs utilized          
                54 context-switches          #    0.005 K/sec                  
                 3 CPU-migrations            #    0.000 K/sec                  
               261 page-faults               #    0.026 K/sec                  
    27,964,187,393 cycles                    #    2.805 GHz                    
    20,902,040,632 stalled-cycles-frontend   #   74.75% frontend cycles idle   
    13,524,565,776 stalled-cycles-backend    #   48.36% backend  cycles idle   
    15,929,463,578 instructions              #    0.57  insns per cycle        
                                             #    1.31  stalled cycles per insn
     2,065,830,063 branches                  #  207.247 M/sec                  
        35,891,035 branch-misses             #    1.74% of all branches        

      10.003882959 seconds time elapsed


Now we use regular memory copy :

# ethtool -K gre1 tx-nocache-copy off
# perf stat netperf -H 7.7.8.84
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 7.7.8.84 () port 0 AF_INET
Recv   Send    Send                          
Socket Socket  Message  Elapsed              
Size   Size    Size     Time     Throughput  
bytes  bytes   bytes    secs.    10^6bits/sec  

 87380  16384  16384    10.00    7706.50   

 Performance counter stats for 'netperf -H 7.7.8.84':

       5708.284991 task-clock                #    0.571 CPUs utilized          
             5,138 context-switches          #    0.900 K/sec                  
                24 CPU-migrations            #    0.004 K/sec                  
               260 page-faults               #    0.046 K/sec                  
    15,990,404,388 cycles                    #    2.801 GHz                    
    10,903,764,099 stalled-cycles-frontend   #   68.19% frontend cycles idle   
     6,089,332,139 stalled-cycles-backend    #   38.08% backend  cycles idle   
    10,680,845,426 instructions              #    0.67  insns per cycle        
                                             #    1.02  stalled cycles per insn
     1,401,663,288 branches                  #  245.549 M/sec                  
        15,380,428 branch-misses             #    1.10% of all branches        

      10.004025020 seconds time elapsed


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