netdev - Re: [PATCH net-next-2.6] inetpeer: lower false sharing effect

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Date:	Thu, 09 Jun 2011 17:03:55 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH net-next-2.6] inetpeer: lower false sharing effect

On Thu, 2011-06-09 at 08:26 +0200, Eric Dumazet wrote:
> Profiles show false sharing in addr_compare() because refcnt/dtime
> changes dirty the first inet_peer cache line, where are lying the keys
> used at lookup time. If many cpus are calling inet_getpeer() and
> inet_putpeer(), or need frag ids, addr_compare() is in 2nd position in
> "perf top".
> 

I've applied both inetpeer patches.  I also no longer have inet_getpeer
and inet_putpeer and addr_compare in my profile.  Instead, neighbor
lookup is now dominant.  See profile below.

When I retest with original 3.0-rc2 kernel, inet_putpeer no longer shows
up, wonder if dst->peer was not set for some reason. 

Tim

-     27.06%     memcached  [kernel.kallsyms]             [k] atomic_add_unless.clone.34
   - atomic_add_unless.clone.34
      - 99.97% neigh_lookup
           __neigh_lookup_errno.clone.17
           arp_bind_neighbour
           rt_intern_hash
           __ip_route_output_key
           ip_route_output_flow
           udp_sendmsg
           inet_sendmsg
           __sock_sendmsg
           sock_sendmsg
           __sys_sendmsg
           sys_sendmsg
           system_call_fastpath
           __sendmsg
-     13.33%     memcached  [kernel.kallsyms]             [k] atomic_dec_and_test
   - atomic_dec_and_test
      - 99.89% dst_destroy
         - dst_release
            - 98.12% skb_dst_drop.clone.55
                 dev_hard_start_xmit
               + sch_direct_xmit
            + 1.88% skb_release_head_state
-      3.26%     memcached  [kernel.kallsyms]             [k] do_raw_spin_lock
   - do_raw_spin_lock
      - 92.24% _raw_spin_lock
         + 41.39% sch_direct_xmit


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