Messages in this thread | | | Subject | Re: kernel performance & profiles under heavy disk I/O | Date | Tue, 21 Mar 2000 12:49:11 +0000 (GMT) | From | Alan Cox <> |
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> 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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