On Wed, 2008-07-02 at 21:59 -0600, Matthew Wilcox wrote: > > > This is true and worth considering carefully. Are IRQ numbers a scarce > resource on PowerPC? They are considerably less scarce than interrupt > vectors are on x86-64. How hard is it to make IRQ numbers an abundent > resource? Is it simply a question of increasing NR_IRQS? Yes, indeed, they aren't really scarce... actually less than the underlying HW vectors in most cases, so it isn't a big issue to add some kind of constraint to the allocator. > This cost should be traded off against the cost of allocating something > like the msix_entry array in each driver that wants to use multiple MSIs, > passing that array around, using it properly, etc. > > It would make some sense to pass nr_irqs all the way down to arch code > and let arch code take care of reserving the block of vectors (aligned > appropriately). That would conserve IRQ numbers, though not vectors. > I think we have to consider excess vectors reserved. If we don't, we > could get into the situation where a device uses more interrupts than > the driver thinks it will and problems ensue. Ok, so I lift my objection there in the sense that allocating a linear array of virtual numbers shouldn't be a problem (somebody remind me to make NR_IRQS a config option one of these days on ppc, or help with just getting rid of irq_desc array alltogether :-) However, do you want to still keep the fact that they are power-of-2 aligned up to the API or can I just do a linear block allocation for virtual number sand require drivers to do the appropriate addition/subtraction to get the N'th one ? I will need to allocate appropriately aligned HW numbers but that's done via different mechanisms (and in some case not even under full linux control, ie, hypervisor/firmware does it on pSeries). > By the way, would people be interested in changing the MSI-X API to get > rid of the msix_entry array? If allocating consecutive IRQs isn't a > problem, then we could switch the MSI-X code to use consecutive IRQs. It would make a lot of code simpler... Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
