[PATCH] D97947: [AArch64] Force runtime unrolling for in-order scheduling models

Mon Apr 19 09:33:32 PDT 2021

SjoerdMeijer added a comment.

In D97947#2698661 <https://reviews.llvm.org/D97947#2698661>, @fhahn wrote:

> In D97947#2698654 <https://reviews.llvm.org/D97947#2698654>, @NickGuy wrote:
>
>>> Can you remind me about the impact of this? I.e., if -mcpu is omitted, we default to generic which is classified, or is using, an in-order schedmodel description on Android?
>>
>> Yep, that's right. Though I don't think it was specific to Android, but AArch64 in general.
>
> So does this mean the new behavior will be the default if no CPU is specified? I'm not sure if we are ready for that yet, unless we are confident that the current heuristics work well for out-of-order cores too. (Last time I benchmarked this for out-of-order cores there were a few notable regressions, but it's been a few months since then)

We have probably two options here:

- Florian is right that we may need some more data on how well the bigger cores like this although it seems you already have some,
- Perhaps alternatively, or as a first step, we can introduce a target feature for this and set this for our smaller in-order-cores for which you have just determined this is a good thing?

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97947/new/

https://reviews.llvm.org/D97947