netdev - Re: [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash table

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Message-ID: <20071101091456.26248ce0@freepuppy.rosehill>
Date:	Thu, 1 Nov 2007 09:14:56 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Andi Kleen <ak@...e.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash
 table

On Thu, 01 Nov 2007 11:16:20 +0100
Eric Dumazet <dada1@...mosbay.com> wrote:

> As done two years ago on IP route cache table (commit 
> 22c047ccbc68fa8f3fa57f0e8f906479a062c426) , we can avoid using one lock per 
> hash bucket for the huge TCP/DCCP hash tables.
> 
> On a typical x86_64 platform, this saves about 2MB or 4MB of ram, for litle 
> performance differences. (we hit a different cache line for the rwlock, but 
> then the bucket cache line have a better sharing factor among cpus, since we 
> dirty it less often)
> 
> Using a 'small' table of hashed rwlocks should be more than enough to provide 
> correct SMP concurrency between different buckets, without using too much 
> memory. Sizing of this table depends on NR_CPUS and various CONFIG settings.
> 
> This patch provides some locking abstraction that may ease a future work using 
>   a different model for TCP/DCCP table.
> 
> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> 
>   include/net/inet_hashtables.h |   40 ++++++++++++++++++++++++++++----
>   net/dccp/proto.c              |   16 ++++++++++--
>   net/ipv4/inet_diag.c          |    9 ++++---
>   net/ipv4/inet_hashtables.c    |    7 +++--
>   net/ipv4/inet_timewait_sock.c |   13 +++++-----
>   net/ipv4/tcp.c                |   11 +++++++-
>   net/ipv4/tcp_ipv4.c           |   11 ++++----
>   net/ipv6/inet6_hashtables.c   |   19 ++++++++-------
>   8 files changed, 89 insertions(+), 37 deletions(-)
> 

Longterm is there any chance of using rcu for this? Seems like
it could be a big win.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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