[Cake] and the bad cpu news on arm is

[Dave Taht]

A worthy optimization to eliminate a useless stat, yes!

(However this code path is not hit very often until you stress out a
system with tons of flows.)

At the moment my crusade is to actually convince the main author and
others here to eliminate nearly every statistic being kept, as well as
the ingress rate estimator, the sqrt cache, the different version of
codel, and a couple other things I laid out in a previous email.....

I do happen to like the set associativity idea, but it's proving
really hard to show its value with any existing tests we have.

Dave Täht
Let's go make home routers and wifi faster! With better software!
https://www.gofundme.com/savewifi


On Sun, Dec 20, 2015 at 9:55 AM, Björn Grönvall <bjorngx at gmail.com> wrote:
> Hi Dave,
>
> The data cache on the wndr3800 and the archer is only 32k bytes. Some arm models also have a small cache.
>
> Since the cake data structures are comparatively large it is important to only bring data into the cache that will actually make a difference when enqueueing.
>
> The attached patch avoids reading data that will not be used. It will also save instructions when there are “q->way_hits”.
>
> N.B. If your arm has a large data cache this change may not make much of a difference.
>
> Cheers,
> /b
>
>
>
>
>
> On 19 Dec 2015, at 21:03, Dave Taht <dave.taht at gmail.com> wrote:
>
>> is that bcake configured via sqm to do 200mbit/20mbit, rings
>> in at 82% idle over a 2 minute period over a 1 minute rrul test.
>> cake, in all it's glory of statistics, extra features, bells, and whistles...
>>
>> is also 82% idle.
>>
>> vs sqm's htb + fq_codel at 86% idle.
>>
>> (in other words, this is not a direct measurement of the code under
>> 'load' but over a large sampling interval comparing idle with the
>> loaded state, AND (sigh) htb + fq_codel uses less cpu. am using the
>> mpstat 1 120 test for this from the openwrt sysstat package)
>>
>> The good news from my perspective:
>>
>> A) that it works at all with linux 4.4rc4 on the linksys 1200ac, which
>> was certainly not the case til last week
>> B) We CAN profile now
>> C) All systems for bandwidth (htb and cake) are accurate to 200mbit at
>> least, on this hardware
>>
>> The bad news from my perspective:
>>
>> A) I ran out of time for this back in august. Really have a ton of
>> wifi work stacked up.
>>
>> B) I'd like to see someone show an instance where cake uses less cpu
>> or is better in any way than htb+ fq_codel.
>>
>> There is a very small latency improvement (.8ms vs 1ms on this path).
>>
>> I do not see any other appreciable difference in cpu usage or network
>> behavior... aside from negative ones.
>>
>> Someone that's saying "ooh cake's better" *please* go measure rrul_be
>> while running "mpstat 1 120" for both sqm with fq_codel and sqm with
>> cake.
>>
>> C) I will try to summon the energy to try it on mips myself, tomorrow.
>>
>> --
>> Dave Täht
>> Let's go make home routers and wifi faster! With better software!
>> https://www.gofundme.com/savewifi
>> _______________________________________________
>> Cake mailing list
>> Cake at lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cake
>
>
> --
>
> Björn Grönvall, bjorngx at gmail.com, Cell +46 70 768 06 35, Jabber/XMPP: bg at kth.se
>
> “The ultimate tragedy is not the oppression and cruelty by the bad people but the silence over that by the good people.”
>
> ― Martin Luther King Jr.
>
>
>