On Mon, 2 Mar 2009, Vadim Lobanov wrote: > On Monday 02 March 2009 09:11:54 Linus Torvalds wrote: > > The thing is, with PIO, a 512-byte disk read ends up doing 256 16-bit word > > reads from the controller, each potentially up to 600ns long (PIO0 > > timings). That's 150ms - for a single sector! > > Out of curiosity, the peanut gallery wishes to ask: > Is the above supposed to be 600us (*1000), or 150us (/1000)? Probably the > latter. Sorry, I was off by a lot. Yes. /1000. The end result ends up being lots better (and I should have realized I did my conversion wrong, because the times ended up being _so_ big), but not better enough - we've had dropped timer interrupts etc on those kinds of machines unless you use "hdparm -u1". Although it porbably does mean that the problem tends to be more in the really bad mode0 case (600ns -> 150us/sector -> milliseconds for multi-sector transfers). I forget what our multi-sector limit is, I think it tends to be 16. So you'll never get _really_ long irq-off times, but "several ms" is still pretty damn bad. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
