[llvm-dev] LLVM-MCA Processor Resources ID

[Pietro D'Ettole via llvm-dev]

Thanks for your detailed response, Andrea! It was exactly what I was
looking for.

Do you have any idea of where in llvm-mca instructions get issued? Because
I now have to block some kind of instructions as part of my resource
strategy.

Have a nice day!

Il giorno dom 13 dic 2020 alle ore 17:02 Andrea Di Biagio <
andrea.dibiagio at gmail.com> ha scritto:

> Hi Pietro,
>
> llvm-mca internally assigns each processor resource unit to a 64-bit mask
> value often referred to as `processor resource mask`.
> This convertion allows llvm-mca to speedup some set operations in the
> ResourceManager using simple bit manipulation.
>
> If I remember correctly, the setCustomStrategy works on processor resource
> masks. So you need a way to map processor resource ID to mask values.
> If you want to know how processor resource units are mapped to processor
> resource masks, then you need to use function `computeProcResourceMasks`
> (defined in llvm/MCA/Support.cpp).
>
> ```
> void computeProcResourceMasks(const MCSchedModel &SM,
>
>
> MutableArrayRef<uint64_t> Masks)
> ```
>
> Array Masks is populated with processor mask values (one per each
> processor resource unit declared by the scheduling model).
>
> You can visualise the mapping between resource IDs and resource masks
> using a debug build of llvm-mca by simply passing flag
> `-debug-only=llvm-mca`. Flag -debug` would work too. However `-debug` is
> much more verbose as it doesn't filter out disassembler debug prints.
>
> Example of processor masks computed by ` computeProcResourceMasks ` for
> -mcpu=btver2:
>
> Command: ` llvm-mca -debug-only=llvm-mca -mcpu=btver2 `
>
> ```
> Processor resource masks:
> [ 0]  - 0x00000000000000 - InvalidUnit
> [ 1]  - 0x00000000000001 - JALU0
> [ 2]  - 0x00000000000002 - JALU1
> [ 3]  - 0x00000000004003 - JALU01
> [ 4]  - 0x00000000000004 - JDiv
> [ 5]  - 0x00000000000008 - JFPA
> [ 6]  - 0x00000000000010 - JFPM
> [ 7]  - 0x00000000000020 - JFPU0
> [ 8]  - 0x00000000000040 - JFPU1
> [ 9]  - 0x00000000008060 - JFPU01
> [10]  - 0x00000000010018 - JFPX
> [11]  - 0x00000000000080 - JLAGU
> [12]  - 0x00000000020280 - JLSAGU
> [13]  - 0x00000000000100 - JMul
> [14]  - 0x00000000000200 - JSAGU
> [15]  - 0x00000000000400 - JSTC
> [16]  - 0x00000000041800 - JVALU
> [17]  - 0x00000000000800 - JVALU0
> [18]  - 0x00000000001000 - JVALU1
> [19]  - 0x00000000002000 - JVIMUL
> ```
>
> Here, each entry is a tuple {  ProcResourceIdx - Mask - ProcResourceName }.
>
> A simple lookup of that array is enough to obtain the mask values for your
> custom strategies.
>
> I hope this helps.
> -Andrea
>
>
> On Sun, Dec 13, 2020 at 2:28 PM Pietro D'Ettole via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi everyone,
>>
>> I need to retrieve the ID of a particular ProcResource from the processor
>> SchedModel but I'm having problems with it.
>> In detail, I aim to attach a custom strategy to a particular resource and
>> to do so I thought to use the ResourceManager::setCustomStrategy()
>> method.
>> I've already got to define my CustomStrategy but I can't retrieve the
>> right ResourceID.
>> I've thought to use the MCProcResourceDesc table inside MCSchedModel, but
>> I'm not sure it'll work.
>>
>> Is that a good idea? Do you have in mind a better one?
>>
>> Thanks!
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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