Re: [PATCH 0/4] Fastboot revisited: Asynchronous function calls

Pavel Machek
2009-01-11T13:14:36Z

On Sun 2009-01-04 10:16:57, Linus Torvalds wrote:
>
>
> On Sun, 4 Jan 2009, Arjan van de Ven wrote:
> >
> > To see this working, I uploaded a "before" and "after" kernel bootchart
> > for one of my testboxes at
> >
> > http://www.fenrus.org/linux/before.svg
> > http://www.fenrus.org/linux/after.svg
>
> Ok, so why does the serial port init take so long? That's a quarter of a
> second for you, which is ridiculous.
>
> I _think_ it's the irq auto-probing, but that's just a guess. The 8250
> driver does some historical crud, like
>
> probe_irq_off(probe_irq_on());
>
> to get rid of any pending irq's, but that should be entirely pointless
> these days. I bet that line basically goes back to pre-history, before we
> made the auto-probing much stabler.
>
> The irq auto-probing itself also has a few excessive delays, like waiting
> for 0.1 s just to wait for spurious interrupts to trigger. Doing the extra
> unnecessary probe makes that doubly expensive.
>
> Does this patch make any difference to you? I'm not at all sure that it's
> the irq probing, but if it is, then this should make the serial probe go
> much faster.

Do serial ports even matter for the netbooks this is targeted at?
Serial ports are gone even on normal notebooks and getting rare at
desktop...

> }
>
> /* forget possible initially masked and pending IRQ */
> - probe_irq_off(probe_irq_on());

Delete the comment, too? :-).

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