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

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Date:	Fri, 25 Oct 2013 11:33:38 +0200
From:	Wolfgang Walter <linux@...m.de>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	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

Am Freitag, 25. Oktober 2013, 10:01:58 schrieb Steffen Klassert:
> On Thu, Oct 24, 2013 at 12:52:58AM +0200, Wolfgang Walter wrote:
> > On Wednesday 23 October 2013 10:06:32 Eric Dumazet wrote:
> > > On Wed, 2013-10-23 at 18:59 +0200, Wolfgang Walter wrote:
> > > > 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.
> > > 
> > > Not needed, because it seems we do not merge this SLUB cache with
> > > another one.
> > 
> > Ok. I can't see xfrm_dst_cache on 32bit-systems, though.
> > 
> > > So please post this information, because I believe the default should be
> > > 65536, not 1024 or 4096
> > 
> > Indeed I already saw higher values, at the moment I see:
> > 
> > # while true; do grep dst /proc/slabinfo ; sleep 1; done
> > xfrm_dst_cache     12636  12636    448   36    4 : tunables    0    0    0
> > : slabdata    351    351      0
> We currently start the garbage collector if we have more than gc_thresh
> (1024) dst entries allocated and refuse new allocations at 2 * gc_thresh.
> 
> So maybe we should set gc_thresh to 32768. Than we can have 65536 dst
> entries in the system (cache + packets in flight) before we refuse
> new allocations. In paticular we can still cache another 32768 dst
> entries after the garbage collector was started. It looks like you
> had never more than 15000 dst entries cached, so a default of 32768
> looks reasonable and should also keep smaller embedded routers happy.

The maximum I saw was 18000. I think 32768 is a good value especially as this 
seems to be the minimum on 3.4.x if you have 512MB ram.

Is it possible to log a warning the first time one hits the limit? Something 
like "xfrm_dst_cache full, consider increasing net.ipv4.xfrm4_gc_thresh and/or 
net.ipv6.xfrm6_gc_thresh"?

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