[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 3:53 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
>> 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.
> 
> That is the fault of Gmail.
> 
>> Besides that
>>
>> if ((wp->flags & BP_MEM_READ) || (prot & PAGE_WRITE))
>>
>> is more readable IMHO.
> 
> Agreed. Please see my updated patch.
> 

Looks ok, but you will likely have to resend it with proper subject and
without any traces of this thread. Otherwise the patch won't be found by
any maintainer.

Jan

> Thanks,
> Jun
> 
> 
> 
> Dont handle write watchpoints on read-only memory access.
> This patch also breaks the searching loop for watchpoint once the
> setup for handling watchpoint later is done.
> 
> Signed-off-by: Jun Koi <junkoi2004@gmail.com>
> 
> 
> diff --git a/exec.c b/exec.c
> index 14d1fd7..6fd859f 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) || (wp->flags & BP_MEM_READ)) {
> +                iotlb = io_mem_watch + paddr;
> +                address |= TLB_MMIO;
> +                break;
> +            }
>          }
>      }



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