Subject: Re: tcp bw in 2.6

From: [email-masked] (Larry McVoy)
Date: Tue, 2 Oct 2007 14:26:08 -0700

On Tue, Oct 02, 2007 at 02:16:56PM -0700, David Miller wrote:
> We absolutely depend upon people like you to report when there are
> anomalies like this.  It's the only thing that scales.

Well cool, finally doing something useful :)

Is this issue no test setup?  Because this does seem like something we'd
want to have work well.

> FWIW I have a t1000 Niagara box and an Ultra45 going through a netgear
> gigabit switch.  I'm getting 85MB/sec in one direction and 10MB/sec in
> the other (using bw_tcp from lmbench3).  

Note that bw_tcp mucks with SND/RCVBUF.  It probably shouldn't, it's been
12 years since that code went in there and I dunno if it is still needed.

> Both are using identical
> broadcom tigon3 gigabit chips and identical current kernels so that is
> a truly strange result.
> 
> I'll investigate, it may be the same thing you're seeing.

Wow, sounds very similar.  In my case I was seeing pretty close to 3x
consistently.  You're more like 8x, but I was all e1000 not broadcom.

And note that sky2 doesn't have this problem.  Does the broadcom do TSO?
And sky2 not?  I noticed a much higher CPU load for sky2.
-- 
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Larry McVoy                lm at bitmover.com           http://www.bitkeeper.com