[PATCH v2] Align SBI trap registers to a nice boundary for performance reasons.

[Samuel Holland]

Hi Raj,

This looks like the right approach. A few comments below on the mechanics of the
patch.

On 2025-02-06 1:22 PM, Raj Vishwanathan wrote:
> Align SBI_TRAP_CONTEXT_SIZE to a multiple of 16 bytes. If it is not
> aligned to 16 bytes for RV64, it can create performance problems.
> Aligning it correctly can fix the performance issues.
> 
> Signed-off-by: Raj Vishwanathan <Raj.Vishwanathan at gmail.com>
> --
> Test: Performance issues seen and fix Verified on FPGA.
> Other methods.
>    Run qemu with monitor to check the SP during cpu_in
>    and cpu_out.
>    Add sbi_printf to the function sbi_trap_handler to check
>    the alignment of sbi_trap_context
> ---
>  include/sbi/sbi_trap.h | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/include/sbi/sbi_trap.h b/include/sbi/sbi_trap.h
> index d5182bf..82e9c08 100644
> --- a/include/sbi/sbi_trap.h
> +++ b/include/sbi/sbi_trap.h
> @@ -112,13 +112,16 @@
>  /** Size (in bytes) of sbi_trap_info */
>  #define SBI_TRAP_INFO_SIZE SBI_TRAP_INFO_OFFSET(last)
>  
> +/** Stack pointer is aligned to 16 bytes */
> +#define STACK_BOUNDARY            16
> +#define ALIGN_TO_BOUNDARY(x,a) (((x) + (a) - 1) & ~((a) - 1))

This is the same as the BIT_ALIGN macro that already exists in sbi_bitops.h.

> +
>  /** Size (in bytes) of sbi_trap_context */
> -#define SBI_TRAP_CONTEXT_SIZE (SBI_TRAP_REGS_SIZE + \
> -			       SBI_TRAP_INFO_SIZE + \
> -			       __SIZEOF_POINTER__)
> +#define SBI_TRAP_CONTEXT_SIZE ALIGN_TO_BOUNDARY((SBI_TRAP_REGS_SIZE + \
> +                               SBI_TRAP_INFO_SIZE + \
> +                               __SIZEOF_POINTER__),STACK_BOUNDARY)

Please follow the existing style (spaces between arguments).

>  
>  #ifndef __ASSEMBLER__
> -

Please don't include unrelated changes in the patch.

Regards,
Samuel

>  #include <sbi/sbi_types.h>
>  #include <sbi/sbi_scratch.h>
>