linux-kernel - Re: [revert] mysql+oltp regression

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Date:	Mon, 11 Aug 2008 09:19:42 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Mike Galbraith <efault@....de>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [revert] mysql+oltp regression

Ingo Molnar wrote:
> * Gregory Haskins <ghaskins@...ell.com> wrote:
>
>   
>>>> Speaking of this: Another patch I submitted to you Ingo (had to do 
>>>> with updating the load_weight inside task_setprio) seems to also 
>>>> have this phenomenon: e.g. its technically correct but further 
>>>> testing has revealed negative repercussions elsewhere.  So please 
>>>> ignore that patch (or revert if you already pulled in, but I don't 
>>>> think you have).  Ill try to look into this issue as well.
>>>>         
>>> ok, under which thread/subject is that? Not queued in tip/sched/* 
>>> yet, correct?
>>>   
>>>       
>> Here is the original thread:
>>
>> http://lkml.org/lkml/2008/7/3/416
>>
>> I do not believe you have queued it anywhere (public anyway) yet.
>>
>> Note I have already invalidated 1/2, and now I am retracting 2/2 as 
>> well.  (1/2 is actually a bogus patch, 2/2 is "technically correct" 
>> but causes ripples in the load balancer that need to be sorted out 
>> first.
>>     
>
> ok, thanks. I'm curious, what are those ripple effects? Stability or 
> performance?
>   

Performance.  I found it while working on my pi series (which fyi I 
should have a v2 refresh for soon, probably today...i am hoping to get 
some review feedback from you on that as well, time permitting of course ;).

Basically the behavior I was observing was that kernel builds via distcc 
would cluster all the cc1 jobs on a single core.  At first I thought my 
pi-series was screwed up, but then I realized I had applied the patch 
referenced above earlier in my development tree, and removing it allowed 
pi to work fine.

I found the problem with in once boot cycle with ftrace (thanks 
Steve!).  Basically newidle balancing was always returning "no 
imbalance" even though I had 32 cc1 threads on 1 core, and 3 idle 
cores.  Clearly not correct!  So I think that by adjusting the load up, 
we throw off the hysteresis built into the load averages and cause the 
system to incorrectly think it's balanced. TBD.

-Greg

> 	Ingo
>   

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