@dtaht 

it's a BCM4359 with bcmdhd driver (amlogic fork).
FullMAC architecture doesn't let us use airtime fairness.
So we did some job to decrease buffering inside the driver, we turned off power_save, roaming, periodic scans, background scanning.
We also use a combination of  fq_codel qdisc for wlan0 interface and BBR tcp congestion algo.

bcmdhd driver do some weird things. According to my limited understanding tx_glom and rx_glom work independently from kernel scatter-gather mechanism. So a bunch of tx frames would be splitted and aligned according to tx_glom bucket size every time we try to send something. 
This chip uses single queue for tx and rx, so according to it's architecture there is no way to achieve low delay with medium and heavy traffic scenarios.
Nowadays many android devices use this driver without any optimizations. And it works awful with pfifofast qdisc which is default for android. 
So much to improve...

P.S.
It looks like the default fq_codel interval (100ms) is not enough for mobile devices in some scenarios.
300ms ought to be enough for everybody. 


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