Re: [Qemu-devel] [PATCH 2/5] tcg: reorganize tb_find_physical loop

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 29/03/16 16:26, Paolo Bonzini wrote:
>
> On 29/03/2016 15:19, Sergey Fedorov wrote:
>> On 22/03/16 17:59, Alex Bennée wrote:
>>> sergey.fedorov@linaro.org writes:
>>>
>>>> From: Paolo Bonzini <pbonzini@redhat.com>
>>>>
>>>> Use a continue statement.
>>>>
>>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>>> [Sergey Fedorov: Fix moving to list head in case of no TB]
>>>> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
>>>> ---
>>>>  cpu-exec.c | 50 +++++++++++++++++++++++++-------------------------
>>>>  1 file changed, 25 insertions(+), 25 deletions(-)
>>>>
>>>> diff --git a/cpu-exec.c b/cpu-exec.c
>>>> index fd92452f16f6..f90482eff778 100644
>>>> --- a/cpu-exec.c
>>>> +++ b/cpu-exec.c
>>>> @@ -225,37 +225,37 @@ static TranslationBlock *tb_find_physical(CPUState *cpu,
>>>>      phys_pc = get_page_addr_code(env, pc);
>>>>      phys_page1 = phys_pc & TARGET_PAGE_MASK;
>>>>      h = tb_phys_hash_func(phys_pc);
>>>> -    ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
>>>> -    for(;;) {
>>>> -        tb = *ptb1;
>>>> -        if (!tb) {
>>>> -            return NULL;
>>>> +    for (ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
>>>> +         (tb = *ptb1) != NULL;
>>>> +         ptb1 = &tb->phys_hash_next) {
>>> I'm not sure I'm keen on the assignment in the for condition clause. I
>>> appreciate the cleansing of the if !tb return exit though. Could we be
>>> cleaner maybe? Here is my attempt:
>>>
>>>     static TranslationBlock *tb_find_physical(CPUState *cpu,
>>>                                               target_ulong pc,
>>>                                               target_ulong cs_base,
>>>                                               uint64_t flags)
>>>     {
>>>         CPUArchState *env = (CPUArchState *)cpu->env_ptr;
>>>         TranslationBlock *tb, **tb_hash_head, **ptb1;
>>>         unsigned int h;
>>>         tb_page_addr_t phys_pc, phys_page1;
>>>
>>>         /* find translated block using physical mappings */
>>>         phys_pc = get_page_addr_code(env, pc);
>>>         phys_page1 = phys_pc & TARGET_PAGE_MASK;
>>>         h = tb_phys_hash_func(phys_pc);
>>>
>>>         /* Start at head of the hash entry */
>>>         ptb1 = tb_hash_head = &tcg_ctx.tb_ctx.tb_phys_hash[h];
>>>         tb = *ptb1;
>>>
>>>         while (tb) {
>>>
>>>             if (tb->pc == pc &&
>>>                 tb->page_addr[0] == phys_page1 &&
>>>                 tb->cs_base == cs_base &&
>>>                 tb->flags == flags) {
>>>
>>>                 if (tb->page_addr[1] == -1) {
>>>                     /* done, we have a match */
>>>                     break;
>>>                 } else {
>>>                     /* check next page if needed */
>>>                     target_ulong virt_page2 = (pc & TARGET_PAGE_MASK)
>>>                         + TARGET_PAGE_SIZE;
>>>                     tb_page_addr_t phys_page2 = get_page_addr_code(env, virt_page2);
>>>
>>>                     if (tb->page_addr[1] == phys_page2) {
>>>                         break;
>>>                     }
>>>                 }
>>>             }
>>>
>>>             ptb1 = &tb->phys_hash_next;
>>>             tb = *ptb1;
>>>         }
>>>
>>>         if (tb) {
>>>             /* Move the TB to the head of the list */
>>>             *ptb1 = tb->phys_hash_next;
>>>             tb->phys_hash_next = *tb_hash_head;
>>>             *tb_hash_head = tb;
>>>         }
>>>         return tb;
>>>     }
>>>
>>> FWIW the compiled code is 9 bytes shorter on my machine.
>> Looks like another attempt to rewrite it. I am wondering whom to
>> attribute as an author, then? :)
> I don't really care. :)

Alex, could you give your s-o-b for your variant of code? Or would you
like to make a patch by yourself?

Kind regards,
Sergey