Re: [XenPPC] [pushed][ppc] process all interrupts that may be in the PIC

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Mar 29, 2006, at 12:58 PM, Hollis Blanchard wrote:

> On Wednesday 29 March 2006 11:34, jimix@xxxxxxxxxxxxxx wrote:
> > changeset:   9665:adf9242cac67
> > user:        jimix@xxxxxxxxxxxxxxxxxxxxx
> > date:        Wed Mar 29 12:31:15 2006 -0500
> > summary:     [ppc] process all interrupts that may be in the PIC
> Linux used to loop until there were no more interrupts pending, but  
> it moved
> away from that behavior. Anton explained there were two reasons for  
> that:
> 1) statistically speaking, there is almost never more than one  
> interrupt
> pendings, and
> 2) the cost of an MMIO to find out if there is another interrupt  
> exceeds the
> cost of taking another EE exception
Things a quite a bit different with Xen:
  1. All IRQs have the same priority.
  2. IRQs routed to domains are EOI'd by the domain, thats a looong  
time, longer then an MMIO
  3. We are trying to fill as many event channel bits as possible  
with this logic.
> Accordingly, I don't like this patch.
Tho, I sort of agree with the Anton's strategy for Linux, I'm pretty  
sure the loop is worth it for Xen.
When we actually get more running we can revisit and profile it.
-JX


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