On 05/13/2013 09:03:17 PM, Kevin Hao wrote:
On Mon, May 13, 2013 at 10:47:17AM -0500, Scott Wood wrote:
> On 05/11/2013 06:26:21 PM, Kevin Hao wrote:
> >In the external proxy facility mode, the interrupt is automatically
> >acknowledged with the same effect as reading the IACK register. So
> >this makes external input interrupt more like edge sensitive. That
> >means we can leave the irq hard enabled when it occurs with irq
soft
> >disabled just like the dec and doorbell interrupt. But the External
> >Proxy Register(EPR) is only considered valid from the time that the
> >external interrupt occurs until MSR[EE] is set to 1. So we have to
> >save the EPR before irq hard enabled.
>
> Is it really worth it?
Maybe. :-)
Compare with the current kernel:
* The overhead is that we need additional load & store the contents
of
the EPR from/to PACA.
There's also mental overhead of the extra complexity. The lazy EE
stuff is already fiddly enough (e.g. the recent KVM patches).
* The bonus is we keep the irq hard enabled when a external
interrupt occurs
with irq soft-disabled. As I know we should leave the irq hard
enabled as
much as possible. This is also the primary reason that we
introduce the
Lazy EE.
I don't think "as much as possible" is a good way to look at it, so
much as "as much as is practical", balanced by also wanting to keep the
code as simple as is practical.
-Scott
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