Re: [RFC][PATCH] irq: remove IRQF_DISABLED

Linus Torvalds
2009-03-02T18:55:55Z

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