Re: [Xen-users] vif interfaces drop packets

[Torsten Vielhak <Torsten@xxxxxxxxxx>]

John Madden schrieb:

Yes, I think so... but I did not notice the hangs during a session but
mostly during the TCP SYN handshake :-o
So in my test scenario the "wget --mirror" hangs mostly during the
connect and not during the transfer of some
    

I see hangs mostly in the middle of ssh sessions -- start up a continuous ping and
watch the packet loss.
  

Just found a document in the xen distribution (docs/src/interface.tex). The subsection about networking is interesting:
e.g.

"Each virtual interface uses two ``descriptor rings'', one for transmit,
the other for receive.  Each descriptor identifies a block of contiguous
physical memory allocated to the domain."

and

"If a domain does not keep its receive ring stocked with empty buffers then
packets destined to it may be dropped.  This provides some defence against
receive livelock problems because an overload domain will cease to receive
further data.  Similarly, on the transmit path, it provides the application
with feedback on the rate at which packets are able to leave the system."

In xen/include/public/io/netif.h the sizes of these buffers are defined as
#define NETIF_TX_RING_SIZE 256
#define NETIF_RX_RING_SIZE 256

Perhaps this is too small for new performance machines. My machine is a Dual Xeon 3.2GHz.
If I have time, I will compile new XEN kernels with greater buffers and see what will happen.

cheers,
Torsten

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