netdev - Re: [PATCH] net: reorder fields of struct socket

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Message-Id: <20090315.195923.109697114.davem@davemloft.net>
Date:	Sun, 15 Mar 2009 19:59:23 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dada1@...mosbay.com
Cc:	kchang@...enacr.com, netdev@...r.kernel.org, bmb@...enacr.com
Subject: Re: [PATCH] net: reorder fields of struct socket

From: Eric Dumazet <dada1@...mosbay.com>
Date: Sat, 14 Mar 2009 10:03:54 +0100

> On x86_64, its rather unfortunate that "wait_queue_head_t wait"
> field of "struct socket" spans two cache lines (assuming a 64
> bytes cache line in current cpus)
> 
> offsetof(struct socket, wait)=0x30
> sizeof(wait_queue_head_t)=0x18
> 
> This might explain why Kenny Chang noticed that his multicast workload
> was performing bad with 64 bit kernels, since more cache lines ping pongs
> were involved.
> 
> This litle patch moves "wait" field next "fasync_list" so that both
> fields share a single cache line, to speedup sock_def_readable()
> 
> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>

Applied, thanks a lot Eric.
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