Erik Stromdahl <[email protected]> wrote:

> Iterating the TX queue and thereby dequeuing all available packets in the
> queue could result in performance penalties on some SMP systems.
> 
> The reason for this is most likely that the per-ac lock (active_txq_lock)
> in mac80211 will be held by the CPU iterating the current queue.
> 
> This will lock up other CPUs trying to push new messages on the TX
> queue.
> 
> Instead of iterating the queue we fetch just one packet at the time,
> resulting in minimal starvation of the other CPUs.
> 
> Reported-by: Yibo Zhao <[email protected]>
> Signed-off-by: Erik Stromdahl <[email protected]>

Like others, I'm not convinced about this either. To me it looks like a quick
workaround instead of properly investigating, and fixing, the root cause. To my
understanding the throughput dip was caused by this commit:

e3148cc5fecf ath10k: fix return value check in wake_tx_q op

So to me it feels like the issue has been there all along, just hidden, and the
fix above just exposed it.

-- 
https://patchwork.kernel.org/patch/10873753/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches


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