Re: [PATCH 1/4] mac80211: Switch to a virtual time-based airtime scheduler

[Yibo Zhao <yiboz@codeaurora.org>]

On 2019-09-18 05:31, Toke Høiland-Jørgensen wrote:
> Yibo Zhao <yiboz@codeaurora.org> writes:
> 
>> From: Toke Høiland-Jørgensen <toke@redhat.com>
>> 
>> This switches the airtime scheduler in mac80211 to use a virtual 
>> time-based
>> scheduler instead of the round-robin scheduler used before. This has a
>> couple of advantages:
>> 
>> - No need to sync up the round-robin scheduler in firmware/hardware 
>> with
>>   the round-robin airtime scheduler.
>> 
>> - If several stations are eligible for transmission we can schedule 
>> both of
>>   them; no need to hard-block the scheduling rotation until the head 
>> of the
>>   queue has used up its quantum.
>> 
>> - The check of whether a station is eligible for transmission becomes
>>   simpler (in ieee80211_txq_may_transmit()).
>> 
>> The drawback is that scheduling becomes slightly more expensive, as we 
>> need
>> to maintain an rbtree of TXQs sorted by virtual time. This means that
>> ieee80211_register_airtime() becomes O(logN) in the number of 
>> currently
>> scheduled TXQs. However, hopefully this number rarely grows too big 
>> (it's
>> only TXQs currently backlogged, not all associated stations), so it
>> shouldn't be too big of an issue.
>> 
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> 
> I'll note that this patch still has the two issues that Felix pointed
> out when I posted the RFC version. Namely:
> 
> - The use of divisions in the fast path. I guess I need to go write 
> some
>   reciprocal-calculation code, since that is also an issue with the AQL
>   patches I linked to before.
> 
> - The fact that we don't count the airtime usage of multicast traffic,
>   which with this series means that the vif TXQ will get priority over
>   the others. I think we agreed to fix this by just adding an airtime
>   v_t to the vif as well and use that for scheduling the TXQ. Does
>   ath10k report airtime usage for multicast as well, or only for
>   stations?
> 
> 
I remember we have Felix' patches reducing the time the lock is held in 
mac80211 for DRR, do we need to integrate it into this version？
> -Toke

-- 
Yibo