Messages in this thread | | | Subject | Re: [PATCH 2/2] x86: get more exact nr_irqs | From | (Eric W. Biederman) | Date | Mon, 04 Jan 2010 11:16:21 -0800 |
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Yinghai Lu <yinghai@kernel.org> writes:
> On Mon, Jan 4, 2010 at 8:55 AM, Eric W. Biederman <ebiederm@xmission.com> wrote: >> 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? >> > > irq_desc is allocated dynamically. > > but irq_desc_ptrs is pointer array, it need to be allocated after > nr_irqs is probed.
If we care about memory use efficiency let's replace irq_desc_ptrs with a rbtree or a radix_tree. Something that moves the memory use penalty onto those machines that have a lot of irqs.
Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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