Thread: Massive interactivity improvement under high I/O load!
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joerg_rw is offline joerg_rw
2011-02-17 , 14:25
Posts: 2,222 | Thanked: 12,651 times | Joined on Mar 2010 @ SOL 3
#36
Originally Posted by nightfire View Post
Generally speaking, Linux is tuned for rotating media, not flash memory. The VM and I/O schedulers try to group I/Os together in a sensible manner, to reduce disk thrashing.

Of course, it's meaningless on the n900; there is no penalty for discontinous I/O.
That's not entirely correct. flash memory has massive penalty on writing randomly to different erase pages. I planned to share a link here, but have to realize I can't find the one good one. Google might help, or ask shadowJK on #maemo IRC. Basically the point is - depending on number of buffers in MMC controller - the writing to a different erase page (wich are sized like e.g 128kb) makes the controller erase a flash-page and write the dirty internal buffer to flash, then read back to buffer the new page addressed, and finally modifies the content of buffer according to the pending IO. So for a sequence like write to 0x10000, 0x50000, 0xB0000 it makes almost no difference if the individual write IO is for 1 byte or 50kB - it's the erasing and rewriting of a whole page that takes xx milliseconds, while IO to the same erase page actually only modifies the RAM buffer in controller and takes no time at all.

Originally Posted by nightfire View Post
I wonder if it would be worth setting some binaries unswappable (ie. phone).
AFAIK a lot of elementary stuff already is mlocked, e.g rtcom-dialer-ui

What we really need is maybe a scheduler (plus kswapd) tailored to fit the exact operation mode and capabilities of the particular flash controller

/j
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Last edited by joerg_rw; 2011-02-17 at 14:59.
 

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