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

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Date:	Thu, 01 Nov 2007 11:16:20 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	"David S. Miller" <davem@...emloft.net>
CC:	Linux Netdev List <netdev@...r.kernel.org>,
	Andi Kleen <ak@...e.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash table

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(-)

View attachment "tcp_ehash_locks.patch" of type "text/plain" (13598 bytes)