netdev - Re: Big performance loss from 3.4.63 to 3.10.13 when routing ipv4

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Date:	Wed, 23 Oct 2013 14:04:34 +0200
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Wolfgang Walter <linux@...m.de>
Cc:	David Miller <davem@...emloft.net>, hannes@...essinduktion.org,
	netdev@...r.kernel.org, klassert@...hematik.tu-chemnitz.de
Subject: Re: Big performance loss from 3.4.63 to 3.10.13 when routing ipv4

On Wed, Oct 23, 2013 at 01:33:14PM +0200, Wolfgang Walter wrote:
> Am Mittwoch, 23. Oktober 2013, 10:12:55 schrieb Steffen Klassert:
> > On Tue, Oct 22, 2013 at 03:46:38PM -0400, David Miller wrote:
> > > 
> > > I think we should resolve this soon, even bumping it to 2048 or 4096
> > > and leaving it at that would be I think acceptable.
> > 
> > Yes, of course. Let's use 4096 as the default for ipv4 and ipv6.
> > I'll take care of it next week.
> > 
> 
> I don't know what this value actually means. But on 3.4.x it is much higher. 
> On a machine with 512MB ram it is 32768, on a machine with 1GB ram it is 
> 262144 and with 16GB ram it is 4194304.
> 

Before  we removed the routing cache, the gc threshold was scaled along
with the maximum routing cache size (ip_rt_max_size). With the routing
cache removal, we lost the possibility to scale with ip_rt_max_size
and we had to choose a static default. Maybe we can try to tweak the
gc threshold again with the available memory somehow later. But to fix
it now, we need to find a reasonable default value. Would a default of
4096 meet your requirements?
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