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

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Message-Id: <20081006.144002.56418911.davem@davemloft.net>
Date:	Mon, 06 Oct 2008 14:40:02 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dada1@...mosbay.com
Cc:	minyard@....org, 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

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.
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