Messages in this thread | | | Date | Fri, 21 Nov 2008 11:09:18 -0800 | From | "Yinghai Lu" <> | Subject | Re: [PATCH 2/2 v3] SGI RTC: add generic timer system interrupt |
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On Fri, Nov 21, 2008 at 10:26 AM, H. Peter Anvin <hpa@zytor.com> wrote: > Dimitri Sivanich wrote: >> >> There are basically two issues with using 'normal IRQs' in cases like this: >> >> - Using normal IRQs would mean we would have an IRQ per cpu. The current >> hard coded maximum, NR_IRQS, is 4352 (NR_VECTORS + (32 * MAX_IO_APICS)). >> On machines with large numbers of cpus and an irq per cpu for each desired >> interrupt, that's a lot of IRQs. In addition, the GRU, will need 2 such >> IRQs per cpu. On 4096 cpu systems, you've already used up more than the >> limit just for that. Until some sort of infrastructure change takes place >> that would potentially allow this to be dynamically increased, such as >> Yinghai Lu's "sparse_irq aka dyn_irq v14" patch, this problem will exist. >> >> Furthermore, the actual runtime limit, nr_irqs, is set to 96 by >> probe_nr_irqs for our configuration. This is because that code assumes all >> vectors are io-apic vectors, not cpu centric vectors like the ones I'm >> talking about. With the current, scheme, even on a 128 cpu system, I'm out >> of IRQs immediately. >> >> - The current infrastructure for requesting vector/IRQ combinations doesn't >> allow one to request an interrupt priority higher than i/o device interrupt >> priorities. Clock event (high resolution timer) code should run at higher >> interrupt priority. > > Okay, so it is a hack pending us taking care of issues in the current > code. #1 we're obviously working on, #2 I need to think some more about > but shouldn't be too hard to fix -- if real, it also affects other > interrupt-driven clock sources.
should just remove probe_nr_irqs.
YH
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