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

Protasevich, Natalie
2005-08-15T04:37:02Z

> On Thursday 04 August 2005 02:22 am, Andi Kleen wrote:
> > On Thu, Aug 04, 2005 at 12:05:50AM -0700, James Cleverdon wrote:
> > > diff -pruN 2.6.12.3/arch/i386/kernel/acpi/boot.c
> > > n12.3/arch/i386/kernel/acpi/boot.c ---
> > > 2.6.12.3/arch/i386/kernel/acpi/boot.c 2005-07-15
> 14:18:57.000000000
> > > -0700 +++ n12.3/arch/i386/kernel/acpi/boot.c 2005-08-04
> > > 00:01:10.199710211 -0700 @@ -42,6 +42,7 @@ static inline void
> > > acpi_madt_oem_check(char *oem_id, char
> > > *oem_table_id) { } extern void __init
> clustered_apic_check(void);
> > > static inline int ioapic_setup_disabled(void) { return 0; }
> > > +extern int gsi_irq_sharing(int gsi);
> > > #include <asm/proto.h>
> > >
> > > #else /* X86 */
> > > @@ -51,6 +52,9 @@ static inline int
> ioapic_setup_disabled( #include
> > > <mach_mpparse.h>
> > > #endif /* CONFIG_X86_LOCAL_APIC */
> > >
> > > +static inline int gsi_irq_sharing(int gsi) { return gsi; }
> >
> > Why is this different for i386/x86-64? It shouldn't.
>
> True. Have added code for i386. Unfortunately, I didn't see
> one file that is shared by both architectures and which is
> included when building with I/O APIC support. So, I
> duplicated the function into io_apic.c
>
> > As a unrelated note we really need to get rid of this whole ifdef
> > block.
> >
> > > +++ n12.3/arch/x86_64/Kconfig 2005-08-03
> 21:31:07.487451167 -0700
> > > @@ -280,13 +280,13 @@ config HAVE_DEC_LOCK
> > > default y
> > >
> > > config NR_CPUS
> > > - int "Maximum number of CPUs (2-256)"
> > > - range 2 256
> > > + int "Maximum number of CPUs (2-255)"
> > > + range 2 255
> > > depends on SMP
> > > - default "8"
> > > + default "16"
> >
> > Don't change the default please.
> >
> > > +static int next_irq = 16;
> >
> > Won't this need a lock for hotplug later?
>
> That's what I thought originally, but maybe not. We
> initialize all RTEs and assign IRQs+vectors fairly early in
> boot, plus store the results in arrays. Thereafter the
> functions just return the preallocated values.
>
> Hmmm... Since the I/O APIC init comes after the other CPUs
> are brought online, and since I don't understand all that the
> MSI driver is trying to accomplish, it might be safer to use
> a spin lock anyway.
>
> > > +
> > > + retry_vector:
> > > + vector = assign_irq_vector(gsi);
> > > +
> > > + /*
> > > + * Sharing vectors means sharing IRQs, so scan irq_vectors for
> > > previous + * use of vector and if found, return that IRQ.
> > > However, we never want + * to share legacy IRQs, which usually
> > > have a different trigger mode + * than PCI.
> > > + */
> >
> > Can we perhaps force such sharing early temporarily even when the
> > table is not filled up? This way we would get better test
> coverage of
> > all of this.
> >
> > That would be later disabled of course.
>
> Suppose I added a static counter and pretended that every
> third non-legacy IRQ needed to be shared?
>
> > Rest looks ok to me.
> >
> > -Andi
>
> Sigh. Have to attach the file again. Sorry about that.
>
> Signed-off-by: James Cleverdon <jamesclv@us.ibm.com>

I think you were going to change this line, which fixed the jumps in the
irq distribution:

--- io_apic.c 2005-08-11 10:14:33.564748923 -0700
+++ io_apic.c.new 2005-08-11 10:15:55.412331115 -0700
@@ -617,7 +617,7 @@ int gsi_irq_sharing(int gsi)
* than PCI.
*/
for (i = 0; i < NR_IRQS; i++)
- if (IO_APIC_VECTOR(i) == vector) {
+ if (IO_APIC_VECTOR(i) == vector && i != gsi) {
if (!platform_legacy_irq(i))
break; /* got one */
IO_APIC_VECTOR(gsi) = 0;
But it's not in this version of the patch.
Thanks,
--Natalie
> --
> James Cleverdon
> IBM LTC (xSeries Linux Solutions)
> {jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot comm
>
>