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

[Jun Koi <junkoi2004@gmail.com>]

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.

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;
+            }
         }
     }