From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
To:     Grant Grundler <grundler@google.com>, Kan Yan <kyan@google.com>
Cc:     Johannes Berg <johannes@sipsolutions.net>, wgong@qti.qualcomm.com,
        wgong@codeaurora.org, ath10k@lists.infradead.org,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH v2 2/2] ath10k: Set sk_pacing_shift to 6 for 11AC WiFi chips
In-Reply-To: <CANEJEGuBoRMBJBOrFOYyPtiJSMfTahrVgTfxZ2ift6Q5uGazFA@mail.gmail.com>
References: <1533724802-30944-1-git-send-email-wgong@codeaurora.org> <1533724802-30944-3-git-send-email-wgong@codeaurora.org> <87sh3pdtpg.fsf@toke.dk> <f185ab8722e84c959b375e606d25a29b@aptaiexm02f.ap.qualcomm.com> <87mutue4y8.fsf@toke.dk> <ef7b317006964c0fa72763bbfc5149e5@aptaiexm02f.ap.qualcomm.com> <CANEJEGvcj9gPT8yy++qvi3hz3t9pAXyeUves06gr+ADfn9Ouhg@mail.gmail.com> <1535967508.3437.31.camel@sipsolutions.net> <87in3m25uu.fsf@toke.dk> <1535975240.3437.61.camel@sipsolutions.net> <878t4i1z74.fsf@toke.dk> <CANEJEGsm_BKM6g2x0+a7_5dBy5jkROs+jEjHmrcneGrMdDK41g@mail.gmail.com> <871sa7ylmi.fsf@toke.dk> <CANEJEGuBoRMBJBOrFOYyPtiJSMfTahrVgTfxZ2ift6Q5uGazFA@mail.gmail.com>
Date:   Thu, 21 Feb 2019 16:42:56 +0100
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Grant Grundler <grundler@google.com> writes:

> On Thu, Sep 6, 2018 at 3:18 AM Toke H=C3=B8iland-J=C3=B8rgensen <toke@tok=
e.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.

Getting the queue size limit patches from ChromeOS ported would
alleviate point 2. I do believe Kan said he'd look into that once the
airtime patches were merged. So Kan, any progress on that front? :)

> What does a "4x increase in memory" mean here? Wen, how much more
> memory does this cause ath10k to use?

I didn't say "memory", I said "buffer size"... :)
I.e., it's the latency impact of the increased buffering I'm worried
about (see above), not the system memory usage.

-Toke