On 07/09/2018 11:44 AM, Marcelo Ricardo Leitner wrote:
On Sat, Jul 07, 2018 at 03:43:55PM +0530, Nishanth Devarajan wrote:
net/sched: add skbprio scheduer
Skbprio (SKB Priority Queue) is a queueing discipline that prioritizes packets
according to their skb->priority field. Under congestion, already-enqueued lower
priority packets will be dropped to make space available for higher priority
packets. Skbprio was conceived as a solution for denial-of-service defenses that
need to route packets with different priorities as a means to overcome DoS
attacks.
Why can't we implement this as a new flag for sch_prio.c?
I don't see why this duplication is needed, especially because it will
only be "slower" (as in, it will do more work) when qdisc is already
full and dropping packets anyway.
sch_prio.c and skbprio diverge on a number of aspects:
1. sch_prio.c supports up to 16 priorities whereas skbprio 64. This
is not just a matter of changing a constant since sch_prio.c doesn't use
skb->priority.
2. sch_prio.c does not have a global limit on the number of packets
on all its queues, only a limit per queue.
3. The queues of sch_prio.c are struct Qdisc, which don't have a
method to drop at its tail.
Given the divergences, adding flags to sch_prio.c will essentially
keep both implementations together instead of being isolated as being
proposed.
On the speed point, there may not be noticeable difference between
both qdiscs because the enqueueing and dequeueing costs of both qdics
are O(1). Notice that the "extra work" (i.e. dropping lower priority
packets) is a key aspect of skbprio since it gives routers a cheap way
to choose which packets to drop during a DoS.
[ ]'s
Michel Machado
