netdev - Re: Linux Route Cache performance tests

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Date:	Mon, 07 Nov 2011 00:08:35 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Paweł Staszewski <pstaszewski@...are.pl>
Cc:	Linux Network Development list <netdev@...r.kernel.org>
Subject: Re: Linux Route Cache performance tests

Le dimanche 06 novembre 2011 à 22:57 +0100, Paweł Staszewski a écrit :
> W dniu 2011-11-06 22:26, Eric Dumazet pisze:
> > Le dimanche 06 novembre 2011 à 21:25 +0100, Paweł Staszewski a écrit :
> >> Yes with this is a little problem i think with kernel 3.1 because
> >> dmesg | egrep  '(rhash)|(route)'
> >> [    0.000000] Command line: root=/dev/md2 rhash_entries=2097152
> >> [    0.000000] Kernel command line: root=/dev/md2 rhash_entries=2097152
> >> [    4.697294] IP route cache hash table entries: 524288 (order: 10,
> >> 4194304 bytes)
> >>
> >>
> > Dont tell me you _still_ use a 32bit kernel ?
> no it is 64bit :)
> Linux localhost 3.1.0 #16 SMP Sun Nov 6 18:09:48 CET 2011 x86_64 Intel(R)
> :)
> 
> > If so, you need to tweak alloc_large_system_hash() to use vmalloc,
> > because you hit MAX_ORDER (10) page allocations.
> funny then :)
> Maybee i turned off too many kernel features
> > But considering LOWMEM is about 700 Mbytes, you wont be able to create a
> > lot of route cache entries.
> >
> > Come on, do us a favor, and enter new era of computing.

OK, then your kernel is not CONFIG_NUMA enabled

It seems strange given you probably have a NUMA machine (24 cpus)

If so, your choices are :

1) enable CONFIG_NUMA. Really this is a must given the workload of your
machine.

2) Or : you need to add "hashdist=1" on boot params
   and patch your kernel with following patch :

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9dd443d..07f86e0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5362,7 +5362,6 @@ int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
 
 int hashdist = HASHDIST_DEFAULT;
 
-#ifdef CONFIG_NUMA
 static int __init set_hashdist(char *str)
 {
 	if (!str)
@@ -5371,7 +5370,6 @@ static int __init set_hashdist(char *str)
 	return 1;
 }
 __setup("hashdist=", set_hashdist);
-#endif
 
 /*
  * allocate a large system hash table from bootmem


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