netdev - Re: [PATCH] net: fix length computation in rt_check

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Date:	Wed, 20 May 2009 06:27:54 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	David Miller <davem@...emloft.net>, jarkao2@...il.com, lav@....ru,
	shemminger@...ux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net: fix length computation in rt_check_expire()

On Wed, May 20, 2009 at 06:54:22AM +0200, Eric Dumazet wrote:
> David Miller a écrit :
> > From: Neil Horman <nhorman@...driver.com>
> > Date: Tue, 19 May 2009 15:24:50 -0400
> > 
> >>> Moving whole group in front would defeat the purpose of move, actually,
> >>> since rank in chain is used to decay the timeout in garbage collector.
> >>> (search for tmo >>= 1; )
> >>>
> >> Argh, so the list is implicitly ordered by expiration time.  That
> >> really defeats the entire purpose of doing grouping in the ilst at
> >> all.  If thats the case, then I agree, its probably better to to
> >> take the additional visitation hit in in check_expire above than to
> >> try and preserve ordering.
> > 
> > Yes, this seems best.
> > 
> > I was worried that somehow the ordering also influences lookups,
> > because the TOS bits don't go into the hash so I worried that it would
> > be important that explicit TOS values appear before wildcard ones.
> > But it doesn't appear that this is an issue, we don't have wildcard
> > TOSs in the rtable entries, they are always explicit.
> > 
> > So I would like to see an explicit final patch from Eric so we can get
> > this fixed now.
> > 
> 
> I would like to split patches because we have two bugs indeed, and
> I prefer to get attention for both problems, I dont remember Neil acknowledged
> the length computation problem.
> 
> First and small patch, candidate for net-2.6 and stable (for 2.6.29) :
> 
> Thank you
> 
> [PATCH] net: fix length computation in rt_check_expire()
> 
> rt_check_expire() computes average and standard deviation of chain lengths,
> but not correclty reset length to 0 at beginning of each chain.
> This probably gives overflows for sum2 (and sum) on loaded machines instead 
> of meaningful results.
> 
> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
Acked-by: Neil Horman <nhorman@...driver.com>

> 
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