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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     leiwa@codeaurora.org
Cc:     ath10k@lists.infradead.org, linux-wireless@vger.kernel.org
Subject: Re: [PATCH v2] ath10k: fix different tx duration output
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References: <1555489045-18070-1-git-send-email-leiwa@codeaurora.org> <87mukprnie.fsf@toke.dk> <298a645b17aac0f5c466f011225533b0@codeaurora.org> <875zrbrb1q.fsf@toke.dk> <ef8c4fec57a8117b98e30c904fc1a3f5@codeaurora.org>
Date:   Tue, 07 May 2019 13:43:52 +0200
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leiwa@codeaurora.org writes:

> On 2019-04-18 16:07, Toke Høiland-Jørgensen wrote:
>> leiwa@codeaurora.org writes:
>> 
>>> On 2019-04-17 17:26, Toke Høiland-Jørgensen wrote:
>>>> Lei Wang <leiwa@codeaurora.org> writes:
>>>> 
>>>>> TX duration output of tx_stats in debugfs and station dump had big
>>>>> difference because they got tx duration value from different 
>>>>> statistic
>>>>> data. We should use the same statistic data.
>>>> 
>>>> So are you sure you picked the most accurate one of the two? :)
>>>> 
>>>> -Toke
>>> 
>>> Hi Toke,
>>> 
>>> Yes.
>>> Now for ath10k, there are two ways to get tx duration output.
>>> One is got from tx_stats in debugfs reported by firmware. It is a 
>>> total
>>> value including all the frames which created by host and firmware sent
>>> to the peer.
>>> And the second is calculated from
>>> ath10k_htt_rx_tx_compl_ind()-->ieee80211_sta_register_airtime(), here
>>> the tx duration just includes the data frames sent from host to the
>>> peer.
>> 
>> So the difference is that the former includes control frames as well? 
>> Is
>> that the only difference? And what exactly is a "big difference" (from
>> the commit message)?
>> 
> Yes,it adds the duration time of receiving ACK frames.
>  From my test,TX from AP to station with iperf UDP test in 
> 10s,tx_stats->tx_duration:5496623us,
> and another value is 3934327us.

Hmm, that's quite a big difference. Is this really only ACKs, or is it
also a question of whether retries are accounted? If so, it may actually
be that what we should do is change which value is passed to
ieee80211_sta_register_airtime()?

>>> So the first value is preferable for station dump.
>> 
>> Hmm, I'm not sure if I agree with this. I specifically added the
>> tx_duration to the station dump to be able to get the values used by 
>> the
>> airtime scheduler. This breaks with this patch.
>> 
>> -Toke
>  From our internal discussing, we will revert this change.

Cool, but see above :)

-Toke