netdev - Re: [PATCH 2/2] udp: RCU handling for Unicast packets.

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Message-ID: <49081D67.3050502@cosmosbay.com>
Date:	Wed, 29 Oct 2008 09:23:03 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Miller <davem@...emloft.net>
CC:	shemminger@...tta.com, benny+usenet@...rsen.dk, minyard@....org,
	netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	Christoph Lameter <cl@...ux-foundation.org>,
	a.p.zijlstra@...llo.nl, johnpol@....mipt.ru,
	Christian Bell <christian@...i.com>
Subject: Re: [PATCH 2/2] udp: RCU handling for Unicast packets.

David Miller a écrit :
> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Tue, 28 Oct 2008 23:45:15 +0100
> 
>> I will submit a new patch serie tomorrow, with :
>>
>> Patch 1 : spinlocks instead of rwlocks, and bug spotted by Christian Bell
>>
>> Patch 2 : splited on two parts (2 & 3) , one for IPV4, one for IPV6, 
> 
> I very much look forward to this :-)
> 
> I like these changes and can't wait to add them to net-next-2.6

Thanks David, please find first updated patch 1

Thanks to Christian Bell and Stephen for their usefull review.

[PATCH] udp: introduce struct udp_table and multiple spinlocks

UDP sockets are hashed in a 128 slots hash table.

This hash table is protected by *one* rwlock.

This rwlock is readlocked each time an incoming UDP message is handled.

This rwlock is writelocked each time a socket must be inserted in
hash table (bind time), or deleted from this table (close time)

This is not scalable on SMP machines :

1) Even in read mode, lock() and unlock() are atomic operations and
 must dirty a contended cache line, shared by all cpus.

2) A writer might be starved if many readers are 'in flight'. This can
 happen on a machine with some NIC receiving many UDP messages. User
 process can be delayed a long time at socket creation/dismantle time.

This patch prepares RCU migration, by introducing 'struct udp_table
and struct udp_hslot', and using one spinlock per chain, to reduce
contention on central rwlock.

Introducing one spinlock per chain reduces latencies, for port
randomization on heavily loaded UDP servers. This also speedup
bindings to specific ports.

udp_lib_unhash() was uninlined, becoming to big.

Some cleanups were done to ease review of following patch
(RCUification of UDP Unicast lookups)

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
---
 include/net/sock.h    |    2
 include/net/udp.h     |   25 ++--
 include/net/udplite.h |    2
 net/ipv4/udp.c        |  209 +++++++++++++++++++++++-----------------
 net/ipv4/udp_impl.h   |    4
 net/ipv4/udplite.c    |   13 +-
 net/ipv6/udp.c        |  112 +++++++++++----------
 net/ipv6/udp_impl.h   |    4
 net/ipv6/udplite.c    |    8 -
 9 files changed, 215 insertions(+), 164 deletions(-)

View attachment "patch_udp_cleanup1.patch" of type "text/plain" (24850 bytes)