Re: [PATCH v2 3/3] powerpc/code-patching: Restore 32-bit patching performance

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 25/03/2024 à 23:48, Benjamin Gray a écrit :
> The new open/close abstraction makes it more difficult for a
> compiler to optimise. This causes 10% worse performance on
> ppc32 as in [1]. Restoring the page alignment mask and inlining
> the helpers allows the compiler to better reason about the address
> alignment, allowing more optimised cache flushing selection.

This should be squashed into patch 1. There is no point in having that 
as a separate patch when in the same series.

> 
> [1]: https://lore.kernel.org/all/77fdcdeb-4af5-4ad0-a4c6-57bf0762dc65@csgroup.eu/
> 
> Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
> 
> ---
> 
> v2: * New in v2
> 
> I think Suggested-by is an appropriate tag. The patch is Christophe's
> from the link, I just added the commit description, so it could well
> be better to change the author to Christophe completely.
> ---
>   arch/powerpc/lib/code-patching.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> index b3a644290369..d089da115987 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -282,13 +282,13 @@ struct patch_window {
>    * Interrupts must be disabled for the entire duration of the patching. The PIDR
>    * is potentially changed during this time.
>    */
> -static int open_patch_window(void *addr, struct patch_window *ctx)
> +static __always_inline int open_patch_window(void *addr, struct patch_window *ctx)
>   {
>   	unsigned long pfn = get_patch_pfn(addr);
>   
>   	lockdep_assert_irqs_disabled();
>   
> -	ctx->text_poke_addr = (unsigned long)__this_cpu_read(cpu_patching_context.addr);
> +	ctx->text_poke_addr = (unsigned long)__this_cpu_read(cpu_patching_context.addr) & PAGE_MASK;
>   
>   	if (!mm_patch_enabled()) {
>   		ctx->ptep = __this_cpu_read(cpu_patching_context.pte);
> @@ -331,7 +331,7 @@ static int open_patch_window(void *addr, struct patch_window *ctx)
>   	return 0;
>   }
>   
> -static void close_patch_window(struct patch_window *ctx)
> +static __always_inline void close_patch_window(struct patch_window *ctx)
>   {
>   	lockdep_assert_irqs_disabled();
>