Messages in this thread | | | Date | Tue, 10 Jan 2023 11:17:39 -0600 | Subject | Re: [PATCH v2] arm64: gic: increase the number of IRQ descriptors | From | Shanker Donthineni <> |
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On 1/10/23 02:20, Marc Zyngier wrote: > External email: Use caution opening links or attachments > > > On Mon, 09 Jan 2023 17:13:25 +0000, > Shanker Donthineni <sdonthineni@nvidia.com> wrote: >> >>>>> I'm happy to help with it, but I'm certainly not willing to accept any >>>>> sort of new compile-time limit. >>>> >>>> Thanks for helping with a scalable solution instead of static >>>> allocation. Please include me whenever patches posted to LKML. I'm >>>> happy to verify on NVIDIA server platforms and provide test >>>> feedback. >>>> >>> >>> I offered to help you. I didn't offer to do the work for you! ;-) >>> >> >> I've looked at the IDR/IDA API. There is no suitable function for >> allocating contiguous IDs to replace bitmap API. >> >> __irq_alloc_descs(): >> >> mutex_lock(&sparse_irq_lock); >> >> start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS, >> from, cnt, 0); >> ret = -EEXIST; >> >> Is there any existing API that I can use for allocating contiguous IDs? > > I think you should address the problem the other way around, as there > are lower hanging fruits: > > - turn the irq_desc_tree radix tree into a XArray > > - use the XArray mark feature to reimplement the irqs_resend bitmap > > Once you have done that, you have already halved the memory usage. > To implement the allocated_irqs bitmap functionality, you have a > bunch of options: > > - make the XArray an allocating XArray, and iterate over XA_FREE_MARK > to find the free range (see how the infiniband subsystem is doing > exactly that) > > - use another Xarray mark to annotate the allocated IRQs, find the > distance between two allocations, and use this range if the request > fits (a poor man's variation of the above) > > - use a sideband data structure such as the GICv3 LPI allocator, which > is already dealing with range allocation (I'd rather avoid that) > > - something else? >
I'll also prototype using XArray data structure instead of IDR based.
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