[Qemu-devel] Re: [PATCH] A bit optimization for tlb_set_page()

[Jan Kiszka <jan.kiszka@web.de>]

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Jun Koi wrote:
> On Wed, Apr 28, 2010 at 8:48 AM, Jun Koi <junkoi2004@gmail.com> wrote:
>> On Wed, Apr 28, 2010 at 3:36 AM, Jan Kiszka <jan.kiszka@web.de> wrote:
>>> Jun Koi wrote:
>>>> It is not necessary to continue searching for watchpoint when we
>>>> already found one and setup for handling watchpoint in a search loop
>>>> in tlb_set_page().
>>>> This patch breaks that search loop on then.
>>> Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>
>>>> Signed-off-by: Jun Koi <junkoi2004@gmail.com>
>>>>
>>>> diff --git a/exec.c b/exec.c
>>>> index 14d1fd7..6329775 100644
>>>> --- a/exec.c
>>>> +++ b/exec.c
>>>> @@ -2240,6 +2240,7 @@ void tlb_set_page(CPUState *env, target_ulong vaddr,
>>>>              /* TODO: The memory case can be optimized by not trapping
>>>>                 reads of pages with a write breakpoint.  */
>>> PS: Don't you also want to address this todo while you are at it? :)
>>>
> 
> Do you have any comment on below patch?
> 
> Thanks,
> J
> 
> 
> Dont handle write watchpoints on read-only memory access.
> This patch also breaks the searching loop for watchpoint once the
> setup facilities for handling watchpoint later is done.
> 
> Signed-off-by: Jun Koi <junkoi2004@gmail.com>
> 
> diff --git a/exec.c b/exec.c
> index 14d1fd7..3f2d9ed 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2236,10 +2236,12 @@ void tlb_set_page(CPUState *env, target_ulong vaddr,
>         watchpoint trap routines.  */
>      QTAILQ_FOREACH(wp, &env->watchpoints, entry) {
>          if (vaddr == (wp->vaddr & TARGET_PAGE_MASK)) {
> -            iotlb = io_mem_watch + paddr;
> -            /* TODO: The memory case can be optimized by not trapping
> -               reads of pages with a write breakpoint.  */
> -            address |= TLB_MMIO;
> +            /* Avoid trapping reads of pages with a write breakpoint. */
> +            if (!((prot & PAGE_WRITE == 0) && (wp->flags &
> BP_MEM_WRITE != 0))) {

Patch is line-wrapped. Besides that

if ((wp->flags & BP_MEM_READ) || (prot & PAGE_WRITE))

is more readable IMHO.

> +                iotlb = io_mem_watch + paddr;
> +                address |= TLB_MMIO;
> +                break;
> +            }
>          }
>      }

Thanks,
Jan


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