From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <dada1@cosmosbay.com>
Subject: Re: [PATCH] iptables: lock free counters
Date: Fri, 20 Feb 2009 00:46:17 +0100
Message-ID: <499DEF49.3040602@cosmosbay.com>
References: <20090218051906.174295181@vyatta.com>	<20090218052747.321329022@vyatta.com> <20090219114719.560999b5@extreme>
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Cc: David Miller <davem@davemloft.net>,
	Patrick McHardy <kaber@trash.net>,
	Rick Jones <rick.jones2@hp.com>, netdev@vger.kernel.org,
	netfilter-devel@vger.kernel.org
To: Stephen Hemminger <shemminger@vyatta.com>
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Stephen Hemminger a =E9crit :
> The reader/writer lock in ip_tables is acquired in the critical path =
of
> processing packets and is one of the reasons just loading iptables ca=
n cause
> a 20% performance loss. The rwlock serves two functions:
>=20
> 1) it prevents changes to table state (xt_replace) while table is in =
use.
>    This is now handled by doing rcu on the xt_table. When table is
>    replaced, the new table(s) are put in and the old one table(s) are=
 freed
>    after RCU period.
>=20
> 2) it provides synchronization when accesing the counter values.
>    This is now handled by swapping in new table_info entries for each=
 cpu
>    then summing the old values, and putting the result back onto one
>    cpu.  On a busy system it may cause sampling to occur at different
>    times on each cpu, but no packet/byte counts are lost in the proce=
ss.
>=20
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>


Acked-by: Eric Dumazet <dada1@cosmosbay.com>

Sucessfully tested on my dual quad core machine too, but iptables only =
(no ipv6 here)

BTW, my new "tbench 8" result is 2450 MB/s, (it was 2150 MB/s not so lo=
ng ago)

Thanks Stephen, thats very cool stuff, yet another rwlock out of kernel=
 :)


>=20
> ---
> Added missing preempt_enable.  Patch against nf-next-2.6 git tree.
>=20
>  include/linux/netfilter/x_tables.h |    6 +
>  net/ipv4/netfilter/arp_tables.c    |  115 ++++++++++++++++++++++++++=
+--------
>  net/ipv4/netfilter/ip_tables.c     |  120 ++++++++++++++++++++++++++=
-----------
>  net/ipv6/netfilter/ip6_tables.c    |  119 +++++++++++++++++++++++++-=
----------
>  net/netfilter/x_tables.c           |   26 ++++++--
>  5 files changed, 284 insertions(+), 102 deletions(-)
>=20