Re: [PATCH] powerpc/mm: use _raw variant of page table accessors

[Balbir Singh <bsingharora@gmail.com>]

On 31/05/16 20:59, Aneesh Kumar K.V wrote:
> This switch few of the page table accessor to use the __raw variant
> and does the cpu to big endian conversion of constants. This helps in
> generating better code.
> 
> For ex: a pgd_none(pgd) check with and without fix is listed below
> 
> Without fix:
> ------------
>    2240:	20 00 61 eb 	ld      r27,32(r1)
> /* PGD level */
> typedef struct { __be64 pgd; } pgd_t;
> static inline unsigned long pgd_val(pgd_t x)
> {
> 	return be64_to_cpu(x.pgd);
> 
>     2244:	22 00 66 78 	rldicl  r6,r3,32,32
>     2248:	3e 40 7d 54 	rotlwi  r29,r3,8
>     224c:	0e c0 7d 50 	rlwimi  r29,r3,24,0,7
>     2250:	3e 40 c5 54 	rotlwi  r5,r6,8
>     2254:	2e c4 7d 50 	rlwimi  r29,r3,24,16,23
>     2258:	0e c0 c5 50 	rlwimi  r5,r6,24,0,7
>     225c:	2e c4 c5 50 	rlwimi  r5,r6,24,16,23
>     2260:	c6 07 bd 7b 	rldicr  r29,r29,32,31
>     2264:	78 2b bd 7f 	or      r29,r29,r5
> 		if (pgd_none(pgd))
>     2268:	00 00 bd 2f 	cmpdi   cr7,r29,0
>     226c:	54 03 9e 41 	beq     cr7,25c0 <__get_user_pages_fast+0x500>
> 
> With fix:
> ---------
>     2370:	20 00 61 eb 	ld      r27,32(r1)
> 		if (pgd_none(pgd))
>     2374:	00 00 bd 2f 	cmpdi   cr7,r29,0
>     2378:	a8 03 9e 41 	beq     cr7,2720 <__get_user_pages_fast+0x530>
> 			break;
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---


Can we just save the cpu_to_be64(_PAGE_PTE) as _BE64_PAGE_PTE constant
in big-endian (pgtable-be-types.h) and similar for other things. I know its
not the best option, but we don't really expect these bits to change often or anymore


Otherwise

Acked-by: Balbir Singh <bsingharora@gmail.com>