Re: [Xen-users] Good unidirectional TCP performance, weird asymetric performance going bidirectional

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, Sep 22, 2008 at 12:00:28AM +0200, Dr. Volker Jaenisch wrote:
> Hi Xen-Users!
> 
> After several hours of tuning and testing I stuck with a serious
> performance degration
> doing bidirectional tcp networking between dom0 to domU as well as domU
> to domU.
> 
> Overview:
> =======
> dom0 to domU:
> -------------------------
> unidirectional :
> dom0 -> domU : 578 Mbits/sec
> dom0 <- domU : 1.22 Gbits/sec
> Cool isnt it?
> 
> bidirectional:
> dom0 <=> domU: 
> dom0 -> domU : 1.22 Gbits/sec
> dom0 <- domU  : 38.2 Mbits/sec
> 
> Ups! But things it can become worse...
> 
> domU1 to domU2:
> ------------------------------
> unidirectional:
> domU1 -> domU2 : 410,2 Mbits/sec
> domU1 <- domU2  : 378.1 Mbits/sec
> Can easily live with that.
> 
> bidirectional:
> domU1 <=> domU2 : 
> domU1 -> domU2 : 42,3 Mbits/sec
> domU1 <- domU2  : 38.2 Mbits/sec
> But what is that?
> 
> Some problems looking similiar to that have been discussed in postings
> in this list and elsewhere. I have read lots of them.
> But none of the mentioned solutions (TCP-tuning, ethtool tweaking, etc)
> have helped to get rid of this behavior.
> May be I missed something.
> 
> This behavior is reproducable with xen 3.1, xen 3.2 on two different
> machines.
> 
> * May anybody confirm this findings?
> * Anybody an idea?
> 

Have you tried changing the vif* interface txqueuelen in dom? I'm wondering
if that would help..

"ifconfig vifX.Y txqueuelen 256" or even bigger value.. default value of 64
isn't too much..

-- Pasi

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