netdev - High perf top ip_idents_reserve doing netperf UDP

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Date:	Wed, 3 Sep 2014 16:59:43 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	brouer@...hat.com,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Florian Westphal <fw@...len.de>
Subject: High perf top ip_idents_reserve doing netperf UDP_STREAM


Hi Eric,

When doing:
 super_netperf 120 -H 192.168.8.2 -t UDP_STREAM -l 100 -- -m 256

I'm seeing function ip_idents_reserve() consuming most CPU.  Could you
help, explain what is going on, and how I can avoid this?

Perf top:
  11.67%  [kernel]   [k] ip_idents_reserve
   8.37%  [kernel]   [k] fib_table_lookup
   4.46%  [kernel]   [k] _raw_spin_lock
   3.21%  [kernel]   [k] copy_user_enhanced_fast_string
   2.92%  [kernel]   [k] sock_alloc_send_pskb
   2.88%  [kernel]   [k] udp_sendmsg

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer
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