I've recently been studying up on the sparc LDom environment and
sunvnet, the virtual network device. In looking through the code I ran
across an odd bit of tx control that I don't quite understand.
Near the bottom of sunvnet_common.c:sunvnet_start_xmit_common(), about
line 1423, just after the ldc_start_done: label is a curious 'if' block
if (unlikely(vnet_tx_dring_avail(dr) < 1)) {
netif_tx_stop_queue(txq);
if (vnet_tx_dring_avail(dr) > VNET_TX_WAKEUP_THRESH(dr))
netif_tx_wake_queue(txq);
}
In order to get into the if-block there needs to be a 0 or negative
return from vnet_tx_dring_avail(), yet then we're checking it again,
with no discernible delay, for a positive value. I don't see how we
could get to the netif_tx_wake_queue() call - shouldn't there be some
delay, or perhaps something that might bump the underlying channel
before checking for more available space?
Perhaps I've missed something?
Thanks,
sln
--
==================================================
Shannon Nelson shannon.nelson@xxxxxxxxxx
Parents can't afford to be squeamish
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