On 10/21/20 11:40 AM, Christophe Leroy wrote:
> 
> 
> Le 21/10/2020 à 17:19, Peter Zijlstra a écrit :
>> On Wed, Oct 21, 2020 at 03:27:18PM +0200, Jakub Jelinek wrote:
>>> Hi!
>>>
>>> Based on the GCC PR97445 discussions, I'd like to propose following change,
>>> which should significantly decrease the amount of code in inline functions
>>> that use ilog2, but as I'm already two decades out of the Linux kernel
>>> development, I'd appreciate if some kernel developer could try that (all
>>> I have done is check that it gives the same results as before) and if it
>>> works submit it for inclusion into the kernel?
>>
>> I'll stick it in my queue and feed it to the robots.
>>
> 
> I did a mpc885_ads_defconfig build with your patch. That's far better, even better than with gcc 9 without the patch.
> 
> I only have two instances of get_order() in vmlinux, one of it is used twice, the other is never user.
> 
> With -Winline, the reason for not inlining is for both because "the call is unlikely and the code size would grow"
> 
> Christophe

Do we want a lib/test_log2.c test?  Although Jakub says that he already
verified that is gives the same results as the previous code.

I ran a (new) lib/test_log2.ko before and after Jakub's patch and got the
same results, although I am not claiming that it has an exhaustive set of
tests in it.  [it is attached]

-- 
~Randy