linux-kernel - Re: CFQ IO scheduler patch series - AIM7 DBase results on a 16-way IA64

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Date:	Mon, 21 May 2007 11:11:10 -0400
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, vtaras@...nvz.org
Subject: Re: CFQ IO scheduler patch series - AIM7 DBase results on a 16-way
   IA64

Jens Axboe wrote:
> On Mon, May 21 2007, Alan D. Brunelle wrote:
>   
>> Jens Axboe wrote:
>>     
>>> On Tue, May 01 2007, Alan D. Brunelle wrote:
>>>  
>>>       
>>>> Jens Axboe wrote:
>>>>    
>>>>         
>>>>> On Mon, Apr 30 2007, Alan D. Brunelle wrote:
>>>>>      
>>>>>           
>>>>>> The results from a single run of an AIM7 DBase load on a 16-way ia64 
>>>>>> box (64GB RAM + 144 FC disks) showed a slight regression (~0.5%) by 
>>>>>> adding in this patch. (Graph can be found at   
>>>>>> http://free.linux.hp.com/~adb/cfq/cfq_dbase.png   ) It is only a single 
>>>>>> set of runs, on a single platform, but it is something to keep an eye 
>>>>>> on as the regression showed itself across the complete run.
>>>>>>        
>>>>>>             
>>>>> Do you know if this regression is due to worse IO performance, or
>>>>> increased system CPU usage?
>>>>>      
>>>>>           
>>>> We performed two point runs yesterday (20,000 and 50,000 tasks) and here 
>>>> are the results:
>>>>
>>>> Kernel  Tasks  Jobs per Minute  %sys (avg)
>>>> ------  -----  ---------------  ----------
>>>> 2.6.21  20000     60,831.1        39.83%
>>>> CFQ br  20000     60,237.4        40.80%
>>>>                   -0.98%        +2.44%
>>>>
>>>> 2.6.21  50000     60,881.6        40.43%
>>>> CFQ br  50000     60,400.6        40.80%
>>>>                   -0.79%        +0.92%
>>>>
>>>> So we're seeing a slight IO performance regression with a slight 
>>>> increase in %system with the CFQ branch. (A chart of the complete run 
>>>> values is up on  http://free.linux.hp.com/~adb/cfq/cfq_20k50k.png  ).
>>>>    
>>>>         
>>> Alan, can you repeat that same run with this patch applied? It
>>> reinstates the cfq lookup hash, which could account for increased system
>>> utilization.
>>>  
>>>       
>> Hi Jens -
>>
>> This test was performed over the weekend, results are updated on
>>
>> http://free.linux.hp.com/~adb/cfq/cfq_dbase.png
>>     
>
> Thanks a lot, Alan! So the cfq hash does indeed improve things a little,
> that's a shame. I guess I'll just reinstate the hash lookup.
>
>   
You're welcome Jens, but remember: It's one set of data; from one 
benchmark; on one architecture; on one platform...don't know if you 
should scrap the whole thing for that! :-) At the very least, I could 
look into trying it out on another architecture. Let me see what I can 
dig up...

Alan
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