On Montag, 10. Januar 2011 Dave Chinner wrote: > Pretty much > every sata disk supports NCQ these days, and default to a depth of > 32, which means we can have 32 concurrent reads in progress at once. > Phase 2 is all synchronous IO, so the only way to hide the IO > latency is to queue work to multiple threads and switch between the > threadsto work on another queue when the current one blocks waiting > for IO. This is interesting. Did you measure this with a rotating single disk? Is the idle time between two synchronous reads bigger than the time needed to move the disk head to another cylinder and read a sector? That takes ~15ms on a normal disk, incredibly long compared to cpu speed. Even with NCQ, the disk would have to swing the head a lot, and just from thinking about it I wouldn't believe that it's faster like this. But I'm sure you tested it so I take it as given that it's like that. Cool improvement, btw :-) -- mit freundlichen Grüssen, Michael Monnerie, Ing. BSc it-management Internet Services: Protéger http://proteger.at [gesprochen: Prot-e-schee] Tel: +43 660 / 415 6531 // ****** Radiointerview zum Thema Spam ****** // http://www.it-podcast.at/archiv.html#podcast-100716 // // Haus zu verkaufen: http://zmi.at/langegg/
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