[Codel] [PATCH v5] pkt_sched: codel: Controlled Delay AQM

[dave taht]

On 05/05/2012 03:09 PM, Eric Dumazet wrote:
> On Sat, 2012-05-05 at 15:03 -0700, dave taht wrote:
>
>> Maybe on your arch, but highly doubtful on a 680Mhz mips that isn't even
>> superscalar.
>>
> CPU are fast, memory is slow.
>
>> I'd prefer to leave it in and be able to compile it out, and actually
>> measure the difference.
> You optimize the case where there is no need to optimize (small queue)
>
> I can see count bigger than 100000 with 20 concurrent netperf
>
> This makes no sense to have a cache so big.
>
> Or there is a bug in codel
The original reciprocol approximation test code rapidly goes AWOL after 
exceeding 2^8.

I went looking for butterflies and didn't see any in the scaled code in 
the range 0-100000,
and they would only take flight briefly, so...

However I have not corrected it for BITS_PER_LONG as per our 4AM 
discussion.

I will get a build going of your latest code with the stats collection 
and look at it harder
after dinner. Get some sleep, too! fun day.

value                      sqrt         recip inv sqrt       relative 
err  scaled inv/sqrt   value      relative err
interval/sqrt(256)=6250000 approx :6250190 1.00003040 interval/scaled: 
6250000 1.00000000
interval/sqrt(257)=6237828 approx :6250190 1.00198178 interval/scaled: 
6238006 1.00002854
interval/sqrt(258)=6225728 approx :6250190 1.00392918 interval/scaled: 
6225870 1.00002281
interval/sqrt(259)=6213697 approx :6250190 1.00587299 interval/scaled: 
6213780 1.00001336
interval/sqrt(260)=6201736 approx :6250190 1.00781297 interval/scaled: 
6201738 1.00000032
interval/sqrt(261)=6189844 approx :6250190 1.00974920 interval/scaled: 
6189929 1.00001373
interval/sqrt(262)=6178020 approx :6250190 1.01168174 interval/scaled: 
6178165 1.00002347
interval/sqrt(263)=6166264 approx :6250190 1.01361051 interval/scaled: 
6166445 1.00002935
interval/sqrt(264)=6154574 approx :6250190 1.01553576 interval/scaled: 
6154585 1.00000179
interval/sqrt(265)=6142951 approx :6250190 1.01745724 interval/scaled: 
6142955 1.00000065
interval/sqrt(266)=6131393 approx :6250190 1.01937521 interval/scaled: 
6131552 1.00002593
interval/sqrt(267)=6119900 approx :6250190 1.02128956 interval/scaled: 
6120009 1.00001781
interval/sqrt(268)=6108472 approx :6250190 1.02320024 interval/scaled: 
6108509 1.00000606
interval/sqrt(269)=6097107 approx :6250190 1.02510748 interval/scaled: 
6097234 1.00002083
interval/sqrt(270)=6085806 approx :6250190 1.02701105 interval/scaled: 
6085819 1.00000214
interval/sqrt(271)=6074567 approx :6250190 1.02891120 interval/scaled: 
6074627 1.00000988
interval/sqrt(272)=6063390 approx :6250190 1.03080785 interval/scaled: 
6063477 1.00001435

...

interval/sqrt(99999)=316229 approx :6250190 19.76475908 interval/scaled: 
316236 1.00002214

>
>