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RE: [Xen-users] Bad TCP accept performance

To: Pasi Kärkkäinen <pasik@xxxxxx>
Subject: RE: [Xen-users] Bad TCP accept performance
From: "Russ Purinton" <rpurinton@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 25 May 2011 11:49:21 -0400
Cc: Carl Byström <cgbystrom@xxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
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Thread-topic: [Xen-users] Bad TCP accept performance
I thought that even traffic still went thru the NIC to loop.  I 
can't seem to find anything on the net supporting this one way or the other, 
though I've seen multiple posts about pinging to test and verify the 
NIC card and drivers working properly.  Not sure what this means.

Also, if it doesn't pass to the NIC, the NIC then the question arises how the 
IP and TCP checksums are being applied if offloading is enabled and it doesn't 
pass thru the NIC.  

I had thought that on a physical host, the loopback ping would hit the network 
card.  I'm guessing with a virtual host, the loopback ping would only hit the 
Virtual NIC but likely not the physical NIC.  If it goes to the virtual NIC, 
then it would be passing thru the PV drivers to the QEMU layer supporting the 
virtual networking right?

The packets shouldn't be visible even from Dom0 because they should stay within 
the vNIC.  Again, not finding any supporting documentation on the 'net, one way 
or the other, so feel free to prove me wrong.


-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Pasi Kärkkäinen
Sent: Wednesday, May 25, 2011 10:08 AM
To: Russ Purinton
Cc: Carl Byström; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Bad TCP accept performance

Using localhost ( goes thru loopback device only, ie. interface 'lo',
so it does NOT go through NIC card or xen/PV drivers..

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