On 02/26/2019 04:56 PM, Eric Dumazet wrote:
>
>
> On 02/26/2019 03:51 PM, Cong Wang wrote:
>> On Tue, Feb 26, 2019 at 3:19 PM Eric Dumazet <eric.duma...@gmail.com> wrote:
>>>
>>>
>>>
>>> On 02/25/2019 10:42 PM, Eric Dumazet wrote:
>>>> HTB + pfifo_fast as a leaf qdisc hits badly the following warning in
>>>> htb_activate() :
>>>>
>>>> WARN_ON(cl->level || !cl->leaf.q || !cl->leaf.q->q.qlen);
>>>>
>>>> This is because pfifo_fast does not update sch->q.qlen, but per cpu
>>>> counters.
>>>> So cl->leaf.q->q.qlen is zero.
>>>>
>>>> HFSC, CBQ, DRR, QFQ have the same problem.
>>>>
>>>> Any ideas how we can fix this ?
>>>
>>> What about something simple for stable ?
>>> ( I yet have to boot/test this )
>>
>> Is merely updating qlen sufficient for fixing it?
>>
>> I thought it is because of the lack of qdisc_tree_reduce_backlog()
>> in pfifo_fast.
>
> It does not seem to be the qdisc_tree_reduce_backlog() thing.
>
> HTB, HFSC, CBQ, DRR, QFQ only peek at their children 'qlen' to decide if there
> is at least one packet in them.
>
> The backlog is only reported for dumps, but the actual backlog value is not
> used in data path.
>
>
Another way to fix this would be to have a shadow version of pfifo_fast, which
basically would be the old version of it, that would be automatically selected
when used as a child of another qdisc (except mq/mqprio of course)
This seems not a stable candidate though.
