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Date:      Tue, 17 Nov 2009 17:19:35 -0800
From:      Chuck Swiger <cswiger@mac.com>
To:        Brett Glass <brett@lariat.net>
Cc:        questions@freebsd.org
Subject:   Re: State of interface polling in FreeBSD
Message-ID:  <B79735ED-EAD6-4C0C-87E8-5302F5E4DB34@mac.com>
In-Reply-To: <200911180032.RAA21582@lariat.net>
References:  <200911180032.RAA21582@lariat.net>

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Hi--

On Nov 17, 2009, at 4:32 PM, Brett Glass wrote:
> I'm building a FreeBSD router based on a small, Intel Atom-based  
> board and am trying to decide whether or not to configure the kernel  
> for polling. What's the current state of interface polling in  
> FreeBSD? Is it worth doing with a single CPU, or will it actually  
> increase system overhead? What "HZ" settings are recommended?

Polling probably works better with a single CPU, compared with doing  
service handling threads per interface, which can do better on SMP  
boxes.  However, the main consideration is probably whether your NICs  
know how to do interrupt mitigation-- if they do, using that is  
probably better than using device polling, at least for low-to- 
moderate network load.  Polling handles high load better; it wastes a  
fair amount of CPU under no to low network load.

The base recommendation is to set HZ to 1000.  If your CPU is having  
problems with that, try 250 or 500 HZ.

Regards,
-- 
-Chuck




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