Re: Conntrack Events Performance - Multipart Messages?

[Fabian Hugelshofer <hugelshofer2006@gmx.ch>]

Fabian Hugelshofer wrote:
> Patrick McHardy wrote:
>> Callgraph information would be useful since its unclear whether
>> this is the memcpy triggered by netlink message trimming in
>> af_netlink.c or something different. Unfortunately according
>> to the documentation this is only supported on x86. I think
>> selecting the netfilter options as modules should provide
>> slightly more detail though.
[...]
> 
> memcpy is mostly invoked by skb_copy and netlink_broadcast (af_netlink). 
> netlink_broadcast is expensive on its own and calls pskb_expand_head 
> which is expensive as well. Using multipart messages would reduce the 
> need to call netlink_broadcast.

I profiled again with nfnetlink and nf_conntrack compiled as modules:
    103599 61.1842 vmlinux
     24481 14.4582 ath_pci
     19232 11.3582 nf_conntrack
     10435  6.1628 wlan
      3588  2.1190 nf_conntrack_netlink
      2869  1.6944 oprofiled
      1886  1.1138 nf_conntrack_ipv4
      1447  0.8546 ath_rate_minstrel
       627  0.3703 nfnetlink
       237  0.1400 ld-uClibc-0.9.29.so
       233  0.1376 libuClibc-0.9.29.so
       183  0.1081 iptable_raw
       174  0.1028 ctevtest
       147  0.0868 busybox
        85  0.0502 libnfnetlink.so.0.2.0
        60  0.0354 libnetfilter_conntrack.so.1.2.0
        38  0.0224 arp_tables
         2  0.0012 arptable_filter

Again most of the time is spent in the kernel. Memory and skb operations 
are accounted there. I suspect that they cause the most overhead.

Do you plan to dig deeper into optimising the non-optimal parts? I 
consider myself not to have enough understanding to do it myself.