Subject: Re: [PATCH] powerpc/mm: Use jump label to speed up radix_enabled check

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 27 Apr 2016 12:30:30 +0530

Benjamin Herrenschmidt <[email-masked]> writes:

> On Wed, 2016-04-27 at 11:00 +1000, Balbir Singh wrote:
>> Just basic testing across CPUs with various mm features 
>> enabled/disabled. Just for sanity
>
> I still don't think it's worth scattering the change. Either the jump
> label works or it doesn't ... The only problem is make sure we identify
> all the pre-boot ones but that's about it.
>

There are two ways to do this. One is to follow the approach listed
below done by Kevin, which is to do the jump_label_init early during boot and
switch both cpu and mmu feature check to plain jump label.

http://mid.gmane.org/[email-masked]

I already found one use case of cpu_has_feature before that
jump_label_init. In this approach we need to carefully audit all the
cpu/mmu_has_feature calls to make sure they don't get called before
jump_label_init. A missed conversion mean we miss a cpu/mmu feature
check.

Other option is to follow the patch I posted above, with the simple
change of renaming mmu_feature_enabled to mmu_has_feature. So we can
use it in early boot without really worrying about when we init jump
label.

What do you suggest we follow ?

-aneesh