Messages in this thread | | | Subject | Re: [PATCH 2/2] x86: get more exact nr_irqs | From | (Eric W. Biederman) | Date | Mon, 04 Jan 2010 08:55:56 -0800 |
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Yinghai Lu <yinghai@kernel.org> writes:
> first check with NR_VECTORS - FIRST_EXTERNAL_VECTOR - 0x20 > aka minus exceptions and system vectors. > > NR_CPUS = 512, and nr_cpu_ids = 128 > will have NR_IRQS = 256 + 512 * 64 = 33024 > > assume we have 20 intel ixgbe 6 port cards (with sriov and ixgbevf) > 20 * 6 * 64 * 3 = 23040 > > first will get: > 128 * (256 - 64) = 24576 > then with nr_irqs_gsi will get > (120 + 8 * 128 + 120 * 256) = 31864 > > so 24576 will be used for nr_irqs. > > 24576 * 8 = 196608 bytes will be used for irq_desc_ptrs[] > > before this patch: > have nr_irqs = 120 + 8 * 128 + 120 * 64 = 8824 > and irq_desc_ptrs[] is 70592 > > Signed-off-by: Yinghai Lu <yinghai@kernel.org>
I am lost. arch_probe_nr_irqs appears to be total nonsense.
We have three concepts. - The number of irq sources we can talk about. ( nr_irqs) - The number of irqs we can possibly service. ((NR_VECTORS - 0x30) *nr_cpu_ids) - The number of irqs we actually connected up to cards in the system that we need to do something with.
Why do we need to allocate arrays at all?
arch_probe_nr_irqs looks like a pile of magic numbers (even more magic with the addition of 0x20), that is always going to be a little bit wrong.
We should be able to remove the arrays all together and allocate irq_desc dynamically.
> --- > arch/x86/kernel/apic/io_apic.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > Index: linux-2.6/arch/x86/kernel/apic/io_apic.c > =================================================================== > --- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c > +++ linux-2.6/arch/x86/kernel/apic/io_apic.c > @@ -3833,15 +3833,20 @@ int __init arch_probe_nr_irqs(void) > { > int nr; > > - if (nr_irqs > (NR_VECTORS * nr_cpu_ids)) > - nr_irqs = NR_VECTORS * nr_cpu_ids; > + /* 0x20 for ipi etc system vectors */ > + nr = NR_VECTORS - FIRST_EXTERNAL_VECTOR - 0x20;
If you are going to subtract of the number of ipis please put appropriate defines in irq_vectors.h. A raw 0x20 is wrong.
> + > + nr *= nr_cpu_ids; > + > + if (nr < nr_irqs) > + nr_irqs = nr; > nr = nr_irqs_gsi + 8 * nr_cpu_ids; > #if defined(CONFIG_PCI_MSI) || defined(CONFIG_HT_IRQ) > /* > * for MSI and HT dyn irq > */ > - nr += nr_irqs_gsi * 64; > + nr += nr_irqs_gsi * 256;
This part seems like magic voodoo. Why should their be a correlation between the number of gsis and the number of msis?
Eric
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