linux-kernel - loaded router, excessive getnstimeofday in oprofile

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Date:	Fri, 22 Aug 2008 04:57:40 +0300
From:	Denys Fedoryshchenko <denys@...p.net.lb>
To:	netdev@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: loaded router, excessive getnstimeofday in oprofile

I have loaded router (~650 Mbps In+Out), based on 2xAMD Opteron 248, Sun Fire 
X4100. HPET timer available (TSC seems not available on this platform).
Network interfaces is onboard, connected over PCI-X.

Right now i am using only one processor, cause using only one interface and 
interrupts stick to it. Other is almost not used.
At peak time i notice in mpstat, that this processor is almost "dead", and if 
i run minor application consuming resources - ping over this router will be 
terrible. For me it is clear - system overloaded. I did oprofile, and here is 
result (at low load time, but at peak time it is very similar).

CPU: AMD64 processors, speed 2193.74 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Cycles outside of halt state) with a unit 
mask of 0x00 (No unit mask) count 100000
CPU_CLK_UNHALT...|
  samples|      %|
------------------
  2679376 71.9851 vmlinux
   287212  7.7163 e1000
   278674  7.4870 ip_tables
   259923  6.9832 nf_conntrack
    29699  0.7979 iptable_nat
    26752  0.7187 nf_nat
    26093  0.7010 nf_conntrack_ipv4
    16525  0.4440 iptable_mangle
    14988  0.4027 oprofiled


CPU: AMD64 processors, speed 2193.74 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Cycles outside of halt state) with a unit 
mask of 0x00 (No unit mask) count 100000
samples  %        symbol name
1031727  37.1736  getnstimeofday
230457    8.3035  __napi_schedule
122154    4.4013  __do_softirq
110036    3.9647  dev_queue_xmit
88800     3.1995  net_rx_action
71163     2.5640  ip_route_input
52232     1.8819  local_bh_enable
43804     1.5783  get_next_timer_interrupt
43387     1.5633  ip_forward
35501     1.2791  nf_iterate
35212     1.2687  __slab_alloc
34652     1.2485  default_idle
32375     1.1665  kfree
28127     1.0134  kmem_cache_alloc

What is bothering me, why getnstimeofday called so much? Even i remove HTB 
shaper, it still takes 30-40% of whole vmlinux time. From other 
applications - only zebra is running.
Any ideas?
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