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Date: Wed, 26 Jul 2006 16:17:45 -0700
From: "Jin Guojun [VFFS]" <jin@george.lbl.gov>
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To: "R. B. Riddick" <arne_woerner@yahoo.com>
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Cc: freebsd-performance@freebsd.org, Raymond Owens <owensr@comcast.net>
Subject: Re: question concerning proper usage of kernel
 variables	net.bpf.bufsize and vm_kmem_size_max
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R. B. Riddick wrote:

>--- Raymond Owens <owensr@comcast.net> wrote:
>  
>
>>Questions:
>>Can VM_KMEM_SIZE_MAX be set manually with sysctl?
>>
>>    
>>
>No, but you could set it with this procedure:
>1. Insert the lines
>  vm.kmem_size=123456789
>  vm.kmem_size_max=1234567890
>in
>  /boot/loader.conf
>
>2. reboot
>
>That should change those values...
>(see src/sys/kern/kern_malloc.c)
>
>I wonder, why your box needs such a big buffer? Do u have network traffic
>bursts or so?
>  
>
Regardless what purpose is for, the net.bpf.bufsize should never
set above hardware cache size. The best (optimal size) is 50% - 80%
of the hardware cache size, unless original BPF is modified in some
way I do not know.
Such high bufsize will degrade performance.

-- 
------------ Jin Guojun ----------- v --- jin@george.lbl.gov ---
Distributed Systems Department		http://www.dsd.lbl.gov/~jin
Lawrence Berkeley National Laboratory,	Berkeley, CA 94720