Re: [PATCH] remove interactive credit

[Bill Davidsen <davidsen@tmr.com>]

Nick Piggin wrote:
> Con Kolivas wrote:
> 
>> remove interactive credit
>>
>>
>>
>> ------------------------------------------------------------------------
>>
>> Special casing tasks by interactive credit was helpful for preventing 
>> fully
>> cpu bound tasks from easily rising to interactive status.
>> However it did not select out tasks that had periods of being fully 
>> cpu bound
>> and then sleeping while waiting on pipes, signals etc. This led to a more
>> disproportionate share of cpu time.
>>
>> Backing this out will no longer special case only fully cpu bound 
>> tasks, and
>> prevents the variable behaviour that occurs at startup before tasks 
>> declare
>> themseleves interactive or not, and speeds up application startup 
>> slightly
>> under certain circumstances. It does cost in interactivity slightly as 
>> load
>> rises but it is worth it for the fairness gains.
>>
>> Signed-off-by: Con Kolivas <kernel@kolivas.org>
>>
> 
> I'm scared :(
> 
> I'm in favour of any attempts to simplify things... but will it be two
> months or three before this spontaneously explodes for half our userbase?
> 
> Andrew's boss so he gets to decide >:)

If I read the intent right, this is an example of worst case avoidance, 
where a little average interactivity is traded for preventing the case 
where a single misguided process gets most/all of the CPU and 
performance falls off the edge of the table. As a user I see that as the 
same line of thought which gave us low-latency patches, to trade a 
miniscule bit of one thing to avoid something really undesirable.

I suspect there will be people who don't want to make this trade, 
although it sounds like a good one to me.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me