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

[Jun Koi <junkoi2004@gmail.com>]

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))) {
+                iotlb = io_mem_watch + paddr;
+                address |= TLB_MMIO;
+                break;
+            }
         }
     }