Re: [PATCH v2 2/2] ath10k: Set sk_pacing_shift to 6 for 11AC WiFi chips - Toke Høiland-Jørgensen

From: "Toke Høiland-Jørgensen" <toke@toke.dk>
To: Kalle Valo <kvalo@codeaurora.org>
Cc: Kan Yan <kyan@google.com>,
	wgong@qti.qualcomm.com, linux-wireless@vger.kernel.org,
	ath10k@lists.infradead.org, Grant Grundler <grundler@google.com>,
	wgong@codeaurora.org, Johannes Berg <johannes@sipsolutions.net>
Subject: Re: [PATCH v2 2/2] ath10k: Set sk_pacing_shift to 6 for 11AC WiFi chips
Date: Thu, 21 Feb 2019 17:28:13 +0100	[thread overview]
Message-ID: <87h8cxhzs2.fsf@toke.dk> (raw)
In-Reply-To: <871s41nmvx.fsf@kamboji.qca.qualcomm.com>

Kalle Valo <kvalo@codeaurora.org> writes:

> Toke Høiland-Jørgensen <toke@toke.dk> writes:
>
>> Grant Grundler <grundler@google.com> writes:
>>
>>> On Thu, Sep 6, 2018 at 3:18 AM Toke Høiland-Jørgensen <toke@toke.dk> wrote:
>>>>
>>>> Grant Grundler <grundler@google.com> writes:
>>>>
>>>> >> And, well, Grant's data is from a single test in a noisy
>>>> >> environment where the time series graph shows that throughput is all over
>>>> >> the place for the duration of the test; so it's hard to draw solid
>>>> >> conclusions from (for instance, for the 5-stream test, the average
>>>> >> throughput for 6 is 331 and 379 Mbps for the two repetitions, and for 7
>>>> >> it's 326 and 371 Mbps) . Unfortunately I don't have the same hardware
>>>> >> used in this test, so I can't go verify it myself; so the only thing I
>>>> >> can do is grumble about it here... :)
>>>> >
>>>> > It's a fair complaint and I agree with it. My counter argument is the
>>>> > opposite is true too: most ideal benchmarks don't measure what most
>>>> > users see. While the data wgong provided are way more noisy than I
>>>> > like, my overall "confidence" in the "conclusion" I offered is still
>>>> > positive.
>>>>
>>>> Right. I guess I would just prefer a slightly more comprehensive
>>>> evaluation to base a 4x increase in buffer size on...
>>>
>>> Kalle, is this why you didn't accept this patch? Other reasons?
>>>
>>> Toke, what else would you like to see evaluated?
>>>
>>> I generally want to see three things measured when "benchmarking"
>>> technologies: throughput, latency, cpu utilization
>>> We've covered those three I think "reasonably".
>>
>> Hmm, going back and looking at this (I'd completely forgotten about this
>> patch), I think I had two main concerns:
>>
>> 1. What happens in a degraded signal situation, where the throughput is
>>    limited by the signal conditions, or by contention with other devices.
>>    Both of these happen regularly, and I worry that latency will be
>>    badly affected under those conditions.
>>
>> 2. What happens with old hardware that has worse buffer management in
>>    the driver->firmware path (especially drivers without push/pull mode
>>    support)? For these, the lower-level queueing structure is less
>>    effective at controlling queueing latency.
>
> Do note that this patch changes behaviour _only_ for QCA6174 and QCA9377
> PCI devices, which IIRC do not even support push/pull mode. All the
> rest, including QCA988X and QCA9984 are unaffected.

Ah, right; I did not go all the way back and look at the actual patch,
so missed that :)

But in that case, why are the latency results that low? Were these tests
done with the ChromeOS queue limit patches?

-Toke

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