netdev - Re: [PATCH 3/3] Convert the UDP hash lock to RCU

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Date:	Mon, 06 Oct 2008 18:08:09 -0500
From:	Corey Minyard <minyard@....org>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, shemminger@...tta.com,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 3/3] Convert the UDP hash lock to RCU

David Miller wrote:
> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Mon, 06 Oct 2008 23:22:31 +0200
>
>   
>> Me wondering what impact this synchronize_rcu() can have on mono-threaded
>> VOIP applications using lot of UDP sockets. What is the maximum delay of
>> this function ?
>>     
>
> The cost is enormous, we really can't use it here.
>
> I have a patch that did top-level socket destruction using RCU,
> and that didn't use synchronize_rcu(), and that killed connection
> rates by up to %20.
>
> I can only imagine what the cost would be if I had to add such a call
> in there.
>
> Really, I can't consider these changes seriously, as-is.
>
>   
Would using SLAB_DESTROY_BY_RCU be ok, or would that be too expensive?

-corey
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