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Date:   Tue, 09 Oct 2018 21:52:37 -0700
From:   Rajkumar Manoharan <rmanohar@codeaurora.org>
To:     =?UTF-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
Cc:     linux-wireless@vger.kernel.org,
        make-wifi-fast@lists.bufferbloat.net, Felix Fietkau <nbd@nbd.name>,
        Kan Yan <kyan@google.com>
Subject: Re: [PATCH RFC v5 3/4] mac80211: Add airtime accounting and
 scheduling to TXQs
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 <153908837900.9471.5394468800857658136.stgit@alrua-kau>
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On 2018-10-09 05:32, Toke Høiland-Jørgensen wrote:
> This adds airtime accounting and scheduling to the mac80211 TXQ
> scheduler. A new callback, ieee80211_sta_register_airtime(), is added
> that drivers can call to report airtime usage for stations.
> 
> When airtime information is present, mac80211 will schedule TXQs
> (through ieee80211_next_txq()) in a way that enforces airtime fairness
> between active stations. This scheduling works the same way as the 
> ath9k
> in-driver airtime fairness scheduling. If no airtime usage is reported
> by the driver, the scheduler will default to round-robin scheduling.
> 
> For drivers that don't control TXQ scheduling in software, a new API
> function, ieee80211_txq_may_transmit(), is added which the driver can 
> use
> to check if the TXQ is eligible for transmission, or should be 
> throttled to
> enforce fairness. Calls to this function must also be enclosed in
> ieee80211_txq_schedule_{start,end}() calls to ensure proper locking. 
> TXQs
> that are throttled by ieee802111_txq_may_transmit() will be woken up 
> again
> by a check added to the ieee80211_wake_txqs() tasklet.
> 

Toke,

I am observing soft lockup issues again with this new series while 
running
traffic with 50 clients. I am continuing testing with earlier series 
along with
snippet I shared. When driver operates in pull-mode, throttled txqs are 
marked
and refilled in airtime_tasklet. This is causing major throughput drops 
and
packet loss and I am suspecting the latency in replenishing deficit.
Whereas in push-mode or in ath9k model, refill happens quicker at every 
packet
indication as well as tx completion.

I am planning to get rid of tasklet completely as it is only meant for 
pull-mode.
It would be better to refill in may_transmit() itself.

-Rajkumar