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


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