> 2.2.5 had significantly greater IO performance and this attachment is
> roughly what changed between 2.2.5 and 2.2.10 or so........
>
> This change has been demonstrated to clobber direct Block-IO with a 50-60%
> penality............just a thought.........
That would make sense for devices with a low block size. Note that part of
the change is a bug fix (clamping to end of media) but the rest of it subtly
changes the I/O pattern so that it wont be reading contiguous bursts of
read-ahead, but instead bursts of read-ahead+random which will mean that
on 1K block I/O you will issue more I/O requests on a dumb controller as
you will tend not to merge 4 requests/page each time.
Andre - if you change it so that the blocks queued to read is clamped
at readahead as before - but keep the overrun check
(ie
blocks = number_user_wants;
if(blocks < readahead)
blocks = readahead;
if(blocks >= the end of the disk)
clamp to end
)
do you get the performance back
-
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