[Qemu-devel] Re: [PATCH 5/5] cache slot lookup

[Avi Kivity]

Glauber Costa wrote:
> record slot used in last lookup. For the common mmio case,
> we'll usually access the same memory slot repeatedly.
>   

> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -75,16 +75,25 @@ static KVMSlot *kvm_alloc_slot(KVMState *s)
>      return NULL;
>  }
>  
> +static KVMSlot *last_slot = NULL;
> +
>  static KVMSlot *kvm_lookup_slot(KVMState *s, target_phys_addr_t start_addr)
>  {
>      int i;
>  
> +
> +    if (last_slot && (start_addr >= last_slot->start_addr &&
> +            start_addr < (last_slot->start_addr + last_slot->memory_size)))
> +        return last_slot;
> +
>      for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
>          KVMSlot *mem = &s->slots[i];
>  
>          if (start_addr >= mem->start_addr &&
> -            start_addr < (mem->start_addr + mem->memory_size))
> +            start_addr < (mem->start_addr + mem->memory_size)) {
> +            last_slot = mem;
>              return mem;
> +        }
>      }
>  

This wasn't introduced by this patch, but the comparison is broken ion 
i386 hosts, where target_phys_addr_t is 32 bits wide.  mem->start_addr + 
mem->memory_size can overflow (this in fact happens for the bios slot at 
4G-128K)

--
error compiling committee.c: too many arguments to function