[PATCH] D64198: [NFC][PowerPC] Add the feature control for PreRA and PostRA scheduler

[Hal Finkel via Phabricator via llvm-commits]

hfinkel added a comment.

In D64198#1570936 <https://reviews.llvm.org/D64198#1570936>, @steven.zhang wrote:

> In D64198#1570920 <https://reviews.llvm.org/D64198#1570920>, @jsji wrote:
>
> > As Hal mentioned, `enable-misched` and `enable-post-misched` should be able to turn on/off the pre-ra/post-ra scheduler.
> >  Regarding to different subtarget (cpu), why we need to turn on/off with feature at runtime? Shouldn't that be configured in code?
> >
> > yeah, per function control might be more useful here.
>
>
> Ah, I didn't realize the option you mentioned, and yes, they can turn on/off the scheduler target independent for all cpu. 
>  But if we want to turn on/off the scheduler for specific cpu, we have to add the feature for it. And the feature supports to be configured at runtime.
>
> I am ok to abandon this patch as I have got the options to turn on/off the scheduler for PowerPC. However, I didn't see the harm to add this feature for PowerPC, as, it is the right way if we want to custom the scheduler for different cpu model. Any thoughts ?


I understand conventional wisdom is that post-RA scheduling is mostly useful for simpler cores, but at least as of the pwr8, it provided a noticeable performance enhancement even for the server-class cores as well. As a result, it seemed to benefit all PowerPC cores we had tested, and so we just had it on for nearly everything. Have you come across cores for which we want it off?


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