From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Erik Stromdahl <erik.stromdahl@gmail.com>, kvalo@qca.qualcomm.com,
        linux-wireless@vger.kernel.org, ath10k@lists.infradead.org
Cc:     yiboz@codeaurora.org
Subject: Re: [PATCH] ath10k: remove iteration in wake_tx_queue
In-Reply-To: <8772dfe6-3f52-05ca-f55a-b7eae14fa7ac@gmail.com>
References: <20190327162906.6010-1-erik.stromdahl@gmail.com> <87bm1qq92j.fsf@toke.dk> <8772dfe6-3f52-05ca-f55a-b7eae14fa7ac@gmail.com>
Date:   Tue, 16 Apr 2019 20:07:27 +0100
Message-ID: <87imvdu5u8.fsf@toke.dk>
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Erik Stromdahl <erik.stromdahl@gmail.com> writes:

> On 4/1/19 1:05 PM, Toke Høiland-Jørgensen wrote:
>> Erik Stromdahl <erik.stromdahl@gmail.com> writes:
>> 
>>> 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.
>> 
>> Did you test this with Felix' patches reducing the time the lock is held
>> in mac80211?
>> 
>> -Toke
>> 
> Hi Toke,
>
> I am not aware of these patches. Can you please point them out for me?

They've already been merged. Commits dcec1d9bc8a7 and 7ef769459f14 in
mac80211-next :)

-Toke