Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]

[Hans Reiser <reiser@namesys.com>]

Andrew Morton wrote:

>
>Large directories tend to be spread all around the disk anyway.  And I've
>never explicitly tested for any problems which the loss of readahead might
>have caused ext2.  Nor have I tested inode table readahead.  Guess I should.
>
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readahead seems to be less effective for non-sequential objects.  Or at 
least, you don't get the order of magnitude benefit from doing only one 
seek, you only get the better elevator scheduling from having more 
things in the elevator, which isn't such a big gain.

For the spectators of the thread, one of the things most of us learn 
from experience about readahead is that there has to be something else 
trying to interject seeks into your workload for readahead to make a big 
difference, otherwise a modern disk drive (meaning, not 30 or so years 
old) is going to optimize it for you anyway using its track cache.

-- 
Hans