Messages in this thread | | | Date | Sat, 28 Jul 2007 00:20:21 +0200 (CEST) | Subject | Re: swap-prefetch: A smart way to make good use of idle resources (was: updatedb) | From | "Indan Zupancic" <> |
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On Sat, July 28, 2007 00:06, Arjan van de Ven wrote: > On Fri, 2007-07-27 at 23:51 +0200, Indan Zupanci >> > also, they take up seek time (5 to 10 msec), so if you were to read >> > something else at the time you get additional latency. >> >> If there's other disk activity swap prefetch shouldn't do much, so this isn't >> really true. > > how do you know there will be other activity? You start the IO and that > basically blacks out the disk for 5 to 10 ms. If the "real" IO gets > submitted in that time you add latency. You cannot predict that IO > happening or not happening.
Ah, in that way. Yes, you right about that (though NCQ might help then?), but that's true for all disk activity. Though I think swap prefetch didn't want to run when there was CPU activity, so that would reduce the chance that new IO is submitted right at that moment. I think in practice this isn't worth worrying about, the real issue is the extra disk activity in the first place.
Greetings,
Indan
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