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

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Date:	Wed, 23 Oct 2013 19:01:57 +0200
From:	Wolfgang Walter <linux@...m.de>
To:	netdev@...r.kernel.org
Cc:	David Miller <davem@...emloft.net>, hannes@...essinduktion.org,
	klassert@...hematik.tu-chemnitz.de
Subject: Fwd: Re: Big performance loss from 3.4.63 to 3.10.13 when routing ipv4

Am Mittwoch, 23. Oktober 2013, 09:17:30 schrieben Sie:
> On Wed, 2013-10-23 at 17:57 +0200, Wolfgang Walter wrote:
> > Am Mittwoch, 23. Oktober 2013, 05:00:01 schrieb Eric Dumazet:
> > > On Wed, 2013-10-23 at 13:33 +0200, Wolfgang Walter wrote:
> > > > 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.
> > > 
> > > Such huge values should not be needed. We should have at most one dst
> > > per packet in flight.
> > > 
> > > On a loaded router, a NIC not using BQL could queue around 16,000
> > > packets.
> > > 
> > > Of course, Qdisc layers could also store a lot of packets, but using the
> > > default pfifo_fast is only adding 1000 packets per interface.
> > > 
> > > I guess using 65536 as the default value should be safe and reasonable
> > > 
> > > Have you tried using 32768 or 65536 ?
> > 
> > I use 32768 on routers with 512MB. They usually have around 50
> > ipsec-tunnels and only about 10 interfaces including vlan-interfaces.
> > 
> > On larger ones I set the bigger values from 3.4.x. That one with 16GB has
> > about 2000 ipsec-tunnels. It has about 80 interfaces (inlcuding vlan-
> > interfaces). Physically it has 8 interfaces with together about 30
> > hardware- queues.
> 
> offlist
> 
> OK, but you do not have the idea of actual number of entries ?
> 
> If you use SLAB, you probably can try "grep dst /proc/slabinfo"

Ah, ok. I use SLUB, but SLABINFO=y.

Without much traffic it is:

# grep dst /proc/slabinfo
xfrm_dst_cache      4435   4608    448   36    4 : tunables    0    0    0 : 
slabdata    128    128      0

on the big one. 

I can recompile the kernels with SLAB instead of SLUB if SLAB gives more 
usefull infos.

Regards,
-- 
Wolfgang Walter
Studentenwerk München
Anstalt des öffentlichen Rechts
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