[PATCH] lib: sbi_domain: Reduce memory usage of per-domain hart context

[Anup Patel]

On Wed, Mar 26, 2025 at 11:51 AM Alvin Chang <alvinga at andestech.com> wrote:
>
> In current implementation, the length of hartindex_to_context_table[]
> array is fixed as SBI_HARTMASK_MAX_BITS. However, the number of harts
> supported by the platform might not be SBI_HARTMASK_MAX_BITS and is
> usually smaller than SBI_HARTMASK_MAX_BITS. This means it is unnecessary
> to allocate such fixed-length array here.
>
> Precisely, current implementation always allocates 1024 bytes for
> hartindex_to_context_table[128] on RV64 platform. However, a platform
> supports two harts only needs hartindex_to_context_table[2], which only
> needs 16 bytes.
>
> This commit calculates needed size of hartindex_to_context_table[]
> according to supported number of harts on the platform when registering
> per-domain data, so that memory usage of per-domain context data can be
> reduced.
>
> Signed-off-by: Alvin Chang <alvinga at andestech.com>
> ---
>  lib/sbi/sbi_domain_context.c | 33 +++++++++++++++++++++------------
>  1 file changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/lib/sbi/sbi_domain_context.c b/lib/sbi/sbi_domain_context.c
> index 407c0d5..0e5c1c2 100644
> --- a/lib/sbi/sbi_domain_context.c
> +++ b/lib/sbi/sbi_domain_context.c
> @@ -53,31 +53,32 @@ struct hart_context {
>         bool initialized;
>  };
>
> -struct domain_context_priv {
> -       /** Contexts for possible HARTs indexed by hartindex */
> -       struct hart_context *hartindex_to_context_table[SBI_HARTMASK_MAX_BITS];
> -};
> -
>  static struct sbi_domain_data dcpriv = {
> -       .data_size = sizeof(struct domain_context_priv),
> +
>  };

No need for the "{ }" as well. I have dropped the "{ }" at the time
of merging this patch.

>
>  static inline struct hart_context *hart_context_get(struct sbi_domain *dom,
>                                                     u32 hartindex)
>  {
> -       struct domain_context_priv *dcp = sbi_domain_data_ptr(dom, &dcpriv);
> +       struct hart_context **dom_hartindex_to_context_table;
> +
> +       dom_hartindex_to_context_table = sbi_domain_data_ptr(dom, &dcpriv);
> +       if (!dom_hartindex_to_context_table || !sbi_hartindex_valid(hartindex))
> +               return NULL;
>
> -       return (dcp && hartindex < SBI_HARTMASK_MAX_BITS) ?
> -               dcp->hartindex_to_context_table[hartindex] : NULL;
> +       return dom_hartindex_to_context_table[hartindex];
>  }
>
>  static void hart_context_set(struct sbi_domain *dom, u32 hartindex,
>                              struct hart_context *hc)
>  {
> -       struct domain_context_priv *dcp = sbi_domain_data_ptr(dom, &dcpriv);
> +       struct hart_context **dom_hartindex_to_context_table;
>
> -       if (dcp && hartindex < SBI_HARTMASK_MAX_BITS)
> -               dcp->hartindex_to_context_table[hartindex] = hc;
> +       dom_hartindex_to_context_table = sbi_domain_data_ptr(dom, &dcpriv);
> +       if (!dom_hartindex_to_context_table || !sbi_hartindex_valid(hartindex))
> +               return;
> +
> +       dom_hartindex_to_context_table[hartindex] = hc;
>  }
>
>  /** Macro to obtain the current hart's context pointer */
> @@ -232,6 +233,14 @@ int sbi_domain_context_exit(void)
>
>  int sbi_domain_context_init(void)
>  {
> +       /**
> +        * Allocate per-domain and per-hart context data.
> +        * The data type is "struct hart_context **" whose memory space will be
> +        * dynamically allocated by domain_setup_data_one(). Calculate needed
> +        * size of memory space here.
> +        */
> +       dcpriv.data_size = sizeof(struct hart_context *) * sbi_hart_count();
> +
>         return sbi_domain_register_data(&dcpriv);
>  }
>
> --
> 2.43.0
>

LGTM.

Reviewed-by: Anup Patel <anup at brainfault.org>

Applied this patch to the riscv/opensbi repo.

Thanks,
Anup