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SubjectLarge IP packets over ArcNet (netif_wake_queue propagation)
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Synopsis:
I am writing test-software for our ArcNet-driver for vxWorks. I use a
Linux machine running 2.4.18 as test-bench. I am trying to test our
rfc1201 (IP over ArcNet) implementation by ping'ing with large packets.
This fails:
Linux simply doesn't send all the IP-fragments.

I then went into the driver and increased the queue-length
from
dev->tx_queue_len = 40;
to
dev->tx_queue_len = 60;
and then it worked.

It seems to me the IP-layer is not notified when the device queue is
emptied by the device and thus doesn't send out the missing fragments.
I tried to look into the net core code to find out: Indeed I could not
find any notification to the higher level protocols.
In vxWorks I am used to waking the higher-level protocols directly
(there is no generic device-specific queue). Thus IP stack can continue
with the next IP-fragment right away. Apparently the Linux IP-stack
can't as it is not notified that the device is ready to send again.

I am really understanding this correctly???

Also, I want to run a raw packet protocol along with IP. That protocol
works best with a small queue - maximum 10 packets!

Esben Nielsen
Vestas Wind Systems


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