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From:   Dave Taht <dave@taht.net>
To:     Wen Gong <wgong@qti.qualcomm.com>
Cc:     "ath10k\@lists.infradead.org" <ath10k@lists.infradead.org>,
        "linux-wireless\@vger.kernel.org" <linux-wireless@vger.kernel.org>
Subject: Re: [PATCH 2/7] ath10k: change max RX bundle size from 8 to 32 for sdio
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        <259d8d7f8c2a4c428ae14ff211c83c1a@aptaiexm02f.ap.qualcomm.com>
Date:   Wed, 04 Sep 2019 06:34:29 -0700
In-Reply-To: <259d8d7f8c2a4c428ae14ff211c83c1a@aptaiexm02f.ap.qualcomm.com>
        (Wen Gong's message of "Wed, 4 Sep 2019 04:43:21 +0000")
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Wen Gong <wgong@qti.qualcomm.com> writes:

>> -----Original Message-----
>> From: Dave Taht <dave@taht.net>
>> Sent: Wednesday, September 4, 2019 12:10 AM
>> To: Wen Gong <wgong@qti.qualcomm.com>; ath10k@lists.infradead.org;
>> linux-wireless@vger.kernel.org
>> Subject: [EXT] Re: [PATCH 2/7] ath10k: change max RX bundle size from 8 to
>> 32 for sdio
>> 
>> 
>> In terms of deeply grokking what increasing buffering to achieve high
>> bandwidth on a testbench, vs what it can do to clobber latency in the
>> real world at low bandwidths, I tend to point folk at:
>> 
>> https://www.youtube.com/watch?v=Rb-UnHDw02o&t=25m40s
>> 
>> where I got a whole bunch of hackers to stand up and act like packets
>> in an aggregating FIFO wifi queue.
>> 
>> This key section is only 8 minutes long, and I promise, y'all laugh
>> at least 3 times at the demonstration.
>> 
>> At the time, also, the ath10k was so overbuffered that on one test
>> I could try to start 100 flows, and only get five.
>> 
>> https://lwn.net/Articles/705884/
>> 
>> and on my slides:
>> 
>> https://blog.linuxplumbersconf.org/2016/ocw//system/presentations/3963/
>> original/linuxplumbers_wifi_latency-3Nov.pdf
>> 
> Hi Dave,
> So your mean is change 8  to 32 will impact latency? It will increase latency of rx?

Heh. for rx, in this case, probably not!

I just get twitchy every time folk fiddle with buffer sizes. In one
recent case someone had fiddled with the interrupt polling interval on
something, going from 1ms to 10ms - it saved on cpu, but...
... just trying to make sure folk grok the tradoffs with a bit of
laughter.

carry on!

>
>> 
>> 0xFFFEFFFF