network performance 6.1 stable vs 4.9

Robert Watson rwatson at FreeBSD.org
Tue May 29 14:51:44 UTC 2007


On Fri, 25 May 2007, Stephen Clark wrote:

> We have a network appliance that is currently based on 4.9. We are in the 
> process of releasing a new version based on 6.1 stable.
>
> In our testing using nttcp thru the appliance we see insignifant difference 
> in thruput between the 2 versions in a controlled environment - aproximately 
> 94mbs on a 100mb lan.
>
> We have a person that is testing the both system inhouse surfing out over 
> the internet on our T1 link and he complains that he is consistently seeing 
> the 6.1 version being much slower than the 4.9 version (on the same 
> hardware). He has been comparing the 6.1 system to 4.9 system for a couple 
> of weeks and continues to insist the 6.1 version is much slower.
>
> Are there any sysctl tunables that may affect performance going over the 
> internet with a slower link, dropped packets, etc that could cause this?
>
> Any ideas would be appreciated.

Steve,

The first thing I'd do is try a double-blind test for your testers -- don't 
tell them which version is running, and then compare performance complaints 
with/without.  This would let you know if there's actually a difference.

The main piece of advice I give people when working with 6.x is to consider 
turning on net.isr.direct, which enables direct dispatch in the network stack. 
With 4.x, I get lower forwarding and processing latency than 6.x unless I 
enable this.  However, my recollection is that you don't want to turn it on on 
releases before 6.1, and I would really be most comfortable turning it on with 
6.2 and later.  In FreeBSD 7.0, net.isr.direct is the default.

You might give that a try and see if it has an effect, but I'd see about 
getting some sort of objective testing of performance going to confirm that 
this isn't a subjectivity issue.

Robert N M Watson
Computer Laboratory
University of Cambridge


>
> Steve
>
> -- 
>
> "They that give up essential liberty to obtain temporary safety, deserve 
> neither liberty nor safety."  (Ben Franklin)
>
> "The course of history shows that as a government grows, liberty decreases." 
> (Thomas Jefferson)
>
>
>
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