netdev - Re: [PATCH net-2.6] Re: rib_trie / Fix inflate_threshold

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Message-ID: <20090702190626.GA2737@ami.dom.local>
Date:	Thu, 2 Jul 2009 21:06:26 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Robert Olsson <robert@...julf.net>
Cc:	Paweł Staszewski <pstaszewski@...are.pl>,
	Linux Network Development list <netdev@...r.kernel.org>,
	Robert Olsson <Robert.Olsson@...a.slu.se>
Subject: Re: [PATCH net-2.6] Re: rib_trie / Fix inflate_threshold_root.
	Now=15 size=11 bits

On Thu, Jul 02, 2009 at 05:31:58PM +0200, Robert Olsson wrote:
> 
> Jarek Poplawski writes:
> 
>  > Yes, it looks like we can't free memory so simple because of such huge
>  > latencies.  
> 
>  Controlling RCU seems crucial. Insertion of the full BGP table increased
>  from 2 seconds to > 20 min with one synchronize_rcu patches.

I wish I knew this a few days before. I could imagine a slow down,
but it looked like it was stuck. Since these last changes weren't
tested on SMP + PREEMPT I thought there is still something broken.
(I was mainly interested in this synchronize_rcu at the moment as
a preemption test.)  

>  And fib_trie "worst case" wrt memory is the root node. So maybe we should 
>  monitor changes in root node and use this to control synchronize_rcu.
> 
>  Didn't Paul suggest something like this?

Sure, and it needs testing, but we should send some safe preemption
fix for -stable first, don't we?

>  And with don't find any decent solution we have to add an option for 
>  a fixed and pre-allocated root-nod typically for BGP-routers.

Probably you're right; I'd prefer to see the test results showing
a difference vs. simply less aggressive root thresholds. But of
course, even if not convinced, I'll respect your choice as the author
and maintainer, so feel free to NAK my proposals - I won't get it
personally.;-)

Cheers,
Jarek P.
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