netdev - [RFC] Make TCP prequeue configurable

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Message-ID: <46FC29E1.9010809@cosmosbay.com>
Date:	Fri, 28 Sep 2007 00:08:33 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Linux Netdev List <netdev@...r.kernel.org>
Subject: [RFC] Make TCP prequeue configurable

Hi all

I am sure some of you are going to tell me that prequeue is not
all black :)

Thank you

[RFC] Make TCP prequeue configurable

The TCP prequeue thing is based on old facts, and has drawbacks.

1) It adds 48 bytes per 'struct tcp_sock'
2) It adds some ugly code in hot paths
3) It has a small hit ratio on typical servers using many sockets
4) It may have a high hit ratio on UP machines running one process,
    where the prequeue adds litle gain. (In fact, letting the user
    doing the copy after being woke up is better for cache reuse)
5) Doing a copy to user in softirq handler is not good, because of
    potential page faults :(
6) Maybe the NET_DMA thing is the only thing that might need prequeue.

This patch introduces a CONFIG_TCP_PREQUEUE, automatically selected if 
CONFIG_NET_DMA is on.

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>


View attachment "net_prequeue.patch" of type "text/plain" (7427 bytes)