[Beowulf] tcp error: Need ideas!
Paulo Afonso Lopes
pal at di.fct.unl.pt
Sat Jan 24 13:57:38 PST 2009
> I wonder if the switch could be implicated. We have seen some (cheap)
> GbE switches not support (in practice) jumbo frames (irrespective of
I got the SMC 8624T because it advertised both Jumbo and link aggregation.
Is this one of the "cheap" you have seen that does not work with Jumbo?
> Nifty Tom Mitchell wrote:
>> On Sat, Jan 24, 2009 at 09:36:09AM -0600, Gerry Creager wrote:
>>> Couple of follow-up notes.
>>> MTU=4500: Had one node fall over with the same overflow errors.
>>> MTU=3000: A WRF model is running, but single timesteps are executing
>>> 2.5x slower than MTU=1500
> Segment offload? Is TSO on or off?
> ethtool -k eth0
> will tell you. You might also have one very reluctant machine, in the
> sense of being unwilling to switch their mtu. Could you do an
> ifconfig eth0 | grep MTU
> on each machine and verify that everyone is using the right MTU?
>>> I'll go snag the new driver and compile it. After all: What can it
>>> Thanks, Guy!
>>> Regards, Gerry
>>> Guy Coates wrote:
>>>> We have also seen problems with the bnx2 drivers.
>>>> I got a more recent set of bnx2 drivers from Broadcom:
>> Has the data been snooped for this data to see if all
>> is as expected.
>> If you are seeing a natural MTU running faster than a jumbo MTU
>> then something is fragmenting or causing fragmentation of the data.
>> Should the MTU=4500 causes overflow errors it might be related to
>> Both the sender and receiver have to keep all the bits on a reliable
>> transfer until the data has been acknowledged. At one time
>> could only be done once to a minimum MTU in the life of a packet.
>> In addition to snooping packets try "tracepath" to and from all
>> the involved boxes to discover what is going on.
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