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
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