netdev - Re: Not understand some in htb_do

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Date:	Tue, 15 Jan 2008 14:54:53 +0100
From:	Martin Devera <devik@....cz>
To:	Badalian Vyacheslav <slavon@...telecom.ru>
CC:	netdev@...r.kernel.org, kaber@...sh.net
Subject: Re: Not understand some in htb_do_events function

Badalian Vyacheslav wrote:
> Martin Devera пишет:
>> Patrick McHardy wrote:
>>> Badalian Vyacheslav wrote:
>>>> Hello all.
>>>> I have many messages like "htb: too many events !" in dmesg.
>>>>
>>>> Try to see code and find that function try do 500 events at call.
>>>> Hm... may anyone ask why 500? Why its not dynamic value based on 
>>>> performance of PC?
>>>
>>>
>>> Thats a good question, I wonder why it is limited at all.
>>> Martin, any hints?
>>>
>>>
>>
>> Hi, I recently replied someone to the same question:
>>
>> > it is possible when during one jiffie (1 or 10ms) more than 500 classes
>> > changed its state. It is meant to protect your system from livelock.
>> > The constant should be set to something like
>> > bogomips/bogocomplexity_of_state_change but it was not done.
>>
>> the solution I have in my mind is to change
>>    if (net_ratelimit())
>>                  printk(KERN_WARNING "htb: too many events !\n");
>>          return HZ/10;
>>  to
>>    return 1;
>>
>> to drain extra events asap. It the time of writing I was not able to
>> come with better solution and there were more bugs related to this
>> part of code than now.
>> We want way to smooth big burst of events over more dequeue invocations
>> in order to not slow dequeue too much. Constant 500 is max. allowed
>> "slowdown" of dequeue.
>> Any bright idea how to do it more elegant, Patrick ?
>>
>> brgds, devik
> 
> Hmm.. i simple see that if i get messages like this in dmesg my PC limit 
> speed, but i have many free CPU and HTB classes have not full bandwidth 
> load....
> If i delete half rules - i get bandwidth that i wont. I wrong understand 
> that if we have this limit (constant 500) my PC can't get full performance?
> 
> Look scheme (example in my memory... not real numbers... for idea only):
> HTB (default 1)
> - Class 1 (rate 250mbs cell 500 prio 1)
> ---- Here 8000 HTB rules (parent 1) (rate 1kbs, cell from 200kbs to 5mbs)
> - Class 2 (rate 250mbs cell 500 prio 1)
> 
> I always go to 2.
> try ttcp.
> current rate in class 1 - above 150mbs
> current rate in class 2 - above 200mbs
> Load avg above 0.10 - 0.25
> Idle - 80%
> 
> Try delete half rules
> current rate in class 1 - above 100mbs
> current rate in class 2 - above 400mbs
> Load avg above 0.10 - 0.25
> Idle - 80%
> 
> All traffic in class 2 do i witch ttcp! its not deleted clients from 
> class 1.
> 
> Any idea? Thanks.

The change above (returning 1 instead of HZ/10) should help, it was tested. Also
you CAN increase the 500 to say 2000. I didn't the change as I'm not sure it is
good generic fix...
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