Re: [PATCH] 2.6.1-mm2: Get irq_vector size right for generic subarch UP installer kernels

[James Cleverdon <jamesclv@us.ibm.com>]

On Tuesday 13 January 2004 5:00 pm, Zwane Mwaikambo wrote:
> On Tue, 13 Jan 2004, James Cleverdon wrote:
> > Problem:  Earlier I didn't consider the case of the generic sub-arch and
> > uni-proc installer kernels used by a number of distros.  It currently is
> > scaled by NR_CPUS.  The correct values should be big for summit and
> > generic, and can stay the same for all others.
>
> This all looks strange, especially in assign_irq_vector() does this
> mean that you'll try and allocate up to 1024 vectors?

The irq_vector array name is a bit misleading.  It contains the vectors for 
each potential I/O APIC RTE.  The array needs to be at least the sum of all 
the RTEs in the system.  Summit PCI bridge chips have large I/O APICs (50 
RTEs), and a large system has up to 16 of them.  16*50 = 800.  Allocating 1k 
entries provides a pad for the future, and u8 doesn't cost much.


> > diff -pru 2.6.1-mm2/include/asm-i386/mach-default/irq_vectors.h
> > t1mm2/include/asm-i386/mach-default/irq_vectors.h
> > --- 2.6.1-mm2/include/asm-i386/mach-default/irq_vectors.h	2004-01-08
> > 22:59:19.000000000 -0800
> > +++ t1mm2/include/asm-i386/mach-default/irq_vectors.h	2004-01-13
> > 13:43:56.000000000 -0800
> > @@ -90,8 +90,12 @@
> >  #else
> >  #ifdef CONFIG_X86_IO_APIC
> >  #define NR_IRQS 224
> > -# if (224 >= 32 * NR_CPUS)
> > -# define NR_IRQ_VECTORS NR_IRQS
> > +/*
> > + * For Summit or generic (i.e. installer) kernels, we have lots of I/O
> > APICs, + * even with uni-proc kernels, so use a big array.
> > + */
> > +# if defined(CONFIG_X86_SUMMIT) || defined(CONFIG_X86_GENERICARCH)
> > +# define NR_IRQ_VECTORS 1024
> >  # else
> >  # define NR_IRQ_VECTORS (32 * NR_CPUS)
> >  # endif

-- 
James Cleverdon
IBM xSeries Linux Solutions
{jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot comm