RE: [RFC][2.6.12.3] IRQ compression/sharing patch

["Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com>]

> > int gsi_irq_sharing(int gsi)
> > {
> >         int i, irq, vector;
> >
> >         BUG_ON(gsi >= NR_IRQ_VECTORS);
> >
> >         if (platform_legacy_irq(gsi)) {
> >                 gsi_2_irq[gsi] = gsi;
> >                 return gsi;
> >         }
> >
> >         if (gsi_2_irq[gsi] != 0xFF)
> >                 return (int)gsi_2_irq[gsi];
> >
> >         vector = assign_irq_vector(gsi); // this part here==========
> 
> I thought I had this case covered earlier, given that in both i386 and
> x86_64:
> 
> #define platform_legacy_irq(irq)      ((irq) < 16)

Yes, you are absolutely correct, I don't need the (gsi<16) part, this
takes care of PCI IRQs that happened to be <16.

> In the deleted vector sharing code, I also check 
> platform_legacy_irq, to avoid inadvertently sharing vectors 
> already assigned to legacy IRQs.
> 
> Am I missing your point here?
> 
> >         if (gsi < 16) {
> >                 irq = gsi;
> >                 gsi_2_irq[gsi] = irq;
> >         } else {
> >                 irq = next_irq++;
> >                 gsi_2_irq[gsi] = irq;
> >         }
> > //====================
> 
> I can't explain the gaps in the numbers with the original 
> version.  I'll give your variant a try.

The only problem is here:

+	if (i < NR_IRQS) {
+		gsi_2_irq[gsi] = i;
+		printk(KERN_INFO "GSI %d sharing vector 0x%02X and IRQ
%d\n",
+				gsi, vector, i);
+		return i;
+	}
+
+	i = next_irq++;
 
That means for any IRQ < NR_IRQS you allow it to be identity mapped,
with all the gaps, and only for ones exceeding 224 you'll assign
consecutive next_irqs++, whereas you can do it for all PCI IRQs above
15. So, the alternative clause should probably come down to just:
                 irq = next_irq++;
                 gsi_2_irq[gsi] = irq; - which means just removing the
one above...
(although we better test that :)...I will definitely test vector sharing
when manage to get on max configuration partition here.

Regards,
--Natalie
 
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