Re: Random file I/O regressions in 2.6

[Alexey Kopytov <alexeyk@mysql.com>]

Ram Pai wrote:
>Without the patch:
>------------------
>Time spent for test:  20.6661s
>
>no of times window reset because of hits: 0
>no of times window reset because of misses: 7
>no of times window was shrunk because of hits: 6716
>no of times the page request was non-contiguous: 5880
>no of times the page request was contiguous : 19639
>
>With the patch:
>--------------
>Time spent for test:  19.5370s
>
>no of times window got reset because of hits: 0
>no of times window got reset because of misses: 0
>no of times window was shrunk because of hits: 5844
>no of times the page request was non-contiguous: 5830
>no of times the page request was contiguous : 20232
>
>Would be nice if Alexey tries the patch on his machine and sees any
>major difference.

Here's what I have (same hardware and test setups):

Without the patch (but with Ram's patch applied):
------------------
Time spent for test: 125.4429s

no of times window reset because of hits: 0
no of times window reset because of misses: 127
no of times window was shrunk because of hits: 1153
no of times the page request was non-contiguous: 3968
no of times the page request was contiguous : 10686

With the patch:
---------------
Time spent for test:  86.5459s

no of times window reset because of hits: 0
no of times window reset because of misses: 0
no of times window was shrunk because of hits: 1066
no of times the page request was non-contiguous: 5860
no of times the page request was contiguous : 18099

I wonder if there are some plans to further improve 2.6 behavior on this 
workload to match that of 2.4? Is the remaing regression a result of the 
different readahead handling, or it might be caused by IDE driver or I/O 
scheduler tuning?

-- 
Alexey Kopytov, Software Developer
MySQL AB, www.mysql.com

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