[Cerowrt-devel] FQ_Codel lwn draft article review
Paul E. McKenney
paulmck at linux.vnet.ibm.com
Mon Dec 3 09:58:49 EST 2012
On Mon, Dec 03, 2012 at 01:54:35PM +0100, Toke Høiland-Jørgensen wrote:
> Dave Taht <dave.taht at gmail.com> writes:
> > you have no control. The tx queue rings are flooded before control is
> > handed back to the fq_codel scheduler. You can get some control back
> > on a non-BQL driver by reducing the number of tx descriptors
> > dramatically, but that leads to issues with small vs big packets....
> Right, so BQL is pretty much a requirement to get anything worthwhile
> out of fq_codel? Or is that too strongly put?
If I understand the code correctly, without BQL, FQ-CoDel does not get
invoked at all.
> Without BQL, exactly how much does the driver queue up? I've heard
> someone say 1000 packets for ethernet, but is that in a different
> context? E.g. pfifo_fast uses /sys/class/net/*/tx_queue_len for queue
> length (I think?), but if the qdisc doesn't, does the driver?
> Toke Høiland-Jørgensen
> toke at toke.dk
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