Re: [Qemu-devel] [PATCH] migration: cache memory region ram ptr

[Paolo Bonzini <pbonzini@redhat.com>]

Il 10/05/2014 12:51, Peter Lieven ha scritto:
> we currently look up the ram ptr for each single page. Cache
> the pointer while we operate on the same block.

Why don't you instead cache the result in the MemoryRegion, so that 
memory_region_get_ram_ptr becomes a simple, inline field access?

Paolo

> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  arch_init.c |   23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/arch_init.c b/arch_init.c
> index 582b716..ce338aa 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -594,13 +594,19 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
>                  ram_bulk_stage = false;
>              }
>          } else {
> +            static uint8_t *ram_ptr;
>              int ret;
>              uint8_t *p;
>              bool send_async = true;
> -            int cont = (block == last_sent_block) ?
> -                RAM_SAVE_FLAG_CONTINUE : 0;
> +            int cont = 0;
>
> -            p = memory_region_get_ram_ptr(mr) + offset;
> +            if (block != last_sent_block) {
> +                ram_ptr = memory_region_get_ram_ptr(mr);
> +            } else {
> +                cont = RAM_SAVE_FLAG_CONTINUE;
> +            }
> +
> +            p = ram_ptr + offset;
>
>              /* In doubt sent page as normal */
>              bytes_sent = -1;
> @@ -990,16 +996,17 @@ static inline void *host_from_stream_offset(QEMUFile *f,
>                                              int flags)
>  {
>      static RAMBlock *block = NULL;
> +    static uint8_t *ram_ptr;
>      char id[256];
>      uint8_t len;
>
>      if (flags & RAM_SAVE_FLAG_CONTINUE) {
> -        if (!block) {
> +        if (!block || !ram_ptr) {
>              fprintf(stderr, "Ack, bad migration stream!\n");
>              return NULL;
>          }
>
> -        return memory_region_get_ram_ptr(block->mr) + offset;
> +        return ram_ptr + offset;
>      }
>
>      len = qemu_get_byte(f);
> @@ -1007,8 +1014,10 @@ static inline void *host_from_stream_offset(QEMUFile *f,
>      id[len] = 0;
>
>      QTAILQ_FOREACH(block, &ram_list.blocks, next) {
> -        if (!strncmp(id, block->idstr, sizeof(id)))
> -            return memory_region_get_ram_ptr(block->mr) + offset;
> +        if (!strncmp(id, block->idstr, sizeof(id))) {
> +            ram_ptr = memory_region_get_ram_ptr(block->mr);
> +            return ram_ptr + offset;
> +        }
>      }
>
>      fprintf(stderr, "Can't find block %s!\n", id);
>