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Message-Id: <20081007.112931.144606424.davem@davemloft.net> Date: Tue, 07 Oct 2008 11:29:31 -0700 (PDT) From: David Miller <davem@...emloft.net> To: a.p.zijlstra@...llo.nl Cc: dada1@...mosbay.com, 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: Peter Zijlstra <a.p.zijlstra@...llo.nl> Date: Tue, 07 Oct 2008 10:31:30 +0200 > On Mon, 2008-10-06 at 14:40 -0700, 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. > > Did you ever figure out why you lost those 20% ? Probably the RCU delay on a 128 cpu machine :-) Also I bet batching the socket destruction eliminates all of the cached local state we have in the cpu at the actual socket destruction time. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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