net_sched: gred: add TCA_GRED_LIMIT attribute
In a GRED qdisc, if the default "virtual queue" (VQ) does not have drop parameters configured, then packets for the default VQ are not subjected to RED and are only dropped if the queue is larger than the net_device's tx_queue_len. This behavior is useful for WRED mode, since these packets will still influence the calculated average queue length and (therefore) the drop probability for all of the other VQs. However, for some drivers tx_queue_len is zero. In other cases the user may wish to make the limit the same for all VQs (including the default VQ with no drop parameters). This change adds a TCA_GRED_LIMIT attribute to set the GRED queue limit, in bytes, during qdisc setup. (This limit is in bytes to be consistent with the drop parameters.) The default limit is the same as for a bfifo queue (tx_queue_len * psched_mtu). If the drop parameters of any VQ are configured with a smaller limit than the GRED queue limit, that VQ will still observe the smaller limit instead. Signed-off-by: NDavid Ward <david.ward@ll.mit.edu> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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