[Cake] small cake_hash optimization?

[Sebastian Moeller]

Hi Pete,

> On Nov 23, 2017, at 10:30, Pete Heist <peteheist at gmail.com> wrote:
> 
> 
>> On Nov 23, 2017, at 9:00 AM, Sebastian Moeller <moeller0 at gmx.de> wrote:
>> 
>> Hi Pete,
>> 
>> 	I should have mentioned "overhead 64 mpu 84" only make sense in combination with a shaper limit (well, they will make sure the cake statistics will be more reflective of what is happening on the ethernet wire, but I am not sure whether that is worth the run-time cost the overhead calculation incurs).
>> 
>> Somewhat unrelated, I wondered about all the excitement about irtt and cloned the repository to my mac, and was absolutely delighted to realize that irtt will also effortlessly work under macos. I only have run the demo from the readme.md with both client and server running at the same machine, but I got results that look reasonable on first sight (but I admit I really do not know exact;y what to expect). This is really great!
> 
> Thanks for the overhead info. I used that in my latest tests. That makes me wonder if those overheads could be defaulted when Cake knows Ethernet is being used with rate limiting? I know a goal is to make cake easier to configure so such things are examples of what people are likely to miss.

	Well, as you note later cake really has no idea what the user wants unless the user actually explicitly requests it. But in your case, I believe instead of the explicit "overhead 38 mpu 84" (I note the 64 above is a typo) you could use the "ethernet" keyword which will under the hood expand to the same values. Personally I am not a big friend of the keywords, but even I admit that they help users lacking the time to dive into the details, especially if the name is as obvious as "ethernet" (all I would wish though would be that these keywords wouls still need to be lead by the "overhead" command, so "overhead ethernet" instead of "ethernet", because that IMHO would be more explicit, but I digress).
Please note that I currently have issues with overhead accounting with on dave's cobalt branch and the new iproute2 tools, automatic kernel overhead accounting does not seem to work at all, so could you please post the output of:
tc -s qdisc
after one of your experiments to confirm that the requested overhead was actually applied?


> 
> Glad to hear irtt runs for you! I was waiting to post something until I clean up some more things in the todo list, but since you found it, let me know (file an Issue) if you find any problems. Also, if you have something later than El Capitan, I might be interested to see the output from “irtt sleep” or ten seconds or so from “irtt clock”, as I’m gradually learning about timer/clock behavior on different OSs. I guess it could also be filed as an Issue, so we don’t add too much to the cake list...

As I am currently on 10.12.6 Sierra, I just went and created two new issues with the requested information; I should note this is a pre-fancy-oled-replacement-for-function-keys macbook pro with a quad 2.5 GHz i7 cpu.

Best Regards
	Sebastian