Messages in this thread | | | Date | Tue, 7 Oct 2008 07:36:11 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 3/3] Convert the UDP hash lock to RCU |
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On Tue, Oct 07, 2008 at 10:31:30AM +0200, Peter Zijlstra wrote: > On Mon, 2008-10-06 at 14:40 -0700, David Miller wrote: > > From: Eric Dumazet <dada1@cosmosbay.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% ? > > > I can only imagine what the cost would be if I had to add such a call > > in there. > > Yeah, sync_rcu() is rediculously expensive, at best 3 jiffies IIRC.
I could make it -much- faster, but at the expense of -serious- CPU overhead. Still, might be useful during boot time (when the system can't do anything useful anyway) to accelerate getting data structures initialized.
Thanx, Paul
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