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From:   Kalle Valo <kvalo@codeaurora.org>
To:     Erik Stromdahl <erik.stromdahl@gmail.com>
Cc:     Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>,
        linux-wireless@vger.kernel.org, ath10k@lists.infradead.org,
        yiboz@codeaurora.org
Subject: Re: [PATCH] ath10k: remove iteration in wake_tx_queue
References: <20190327162906.6010-1-erik.stromdahl@gmail.com>
        <87bm1qq92j.fsf@toke.dk>
        <8772dfe6-3f52-05ca-f55a-b7eae14fa7ac@gmail.com>
        <87imvdu5u8.fsf@toke.dk>
        <f915fa20-a4e1-7312-dea2-d60b716e4877@gmail.com>
Date:   Fri, 26 Apr 2019 10:07:03 +0300
In-Reply-To: <f915fa20-a4e1-7312-dea2-d60b716e4877@gmail.com> (Erik
        Stromdahl's message of "Wed, 17 Apr 2019 15:29:41 +0200")
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Erik Stromdahl <erik.stromdahl@gmail.com> writes:

> On 4/16/19 9:07 PM, Toke H=C3=B8iland-J=C3=B8rgensen wrote:
>> Erik Stromdahl <erik.stromdahl@gmail.com> writes:
>>
>>> On 4/1/19 1:05 PM, Toke H=C3=B8iland-J=C3=B8rgensen 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_l=
ock)
>>>>> 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 he=
ld
>>>> 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
>>
>
> I see. I am using the ath tree and I couldn't find them there.
> I can cherry-pick them to my own tree and try them out
> (or wait until Kalle updates ath.git).

It will take a while before these commits trickle down to ath-next
branch, most likely after v5.2-rc1 is released.

--=20
Kalle Valo