Re: [PATCH 1/2] cpu: use ROUND_UP() to define xxx_PAGE_ALIGN

[Wei Yang <richardw.yang@linux.intel.com>]

On Sun, Oct 13, 2019 at 11:56:35AM -0400, Richard Henderson wrote:
>On 10/12/19 10:11 PM, Wei Yang wrote:
>> Use ROUND_UP() to define, which is a little bit easy to read.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> ---
>>  include/exec/cpu-all.h | 7 +++----
>>  1 file changed, 3 insertions(+), 4 deletions(-)
>> 
>> diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
>> index ad9ab85eb3..255bb186ac 100644
>> --- a/include/exec/cpu-all.h
>> +++ b/include/exec/cpu-all.h
>> @@ -220,7 +220,7 @@ extern int target_page_bits;
>>  
>>  #define TARGET_PAGE_SIZE (1 << TARGET_PAGE_BITS)
>>  #define TARGET_PAGE_MASK ~(TARGET_PAGE_SIZE - 1)
>> -#define TARGET_PAGE_ALIGN(addr) (((addr) + TARGET_PAGE_SIZE - 1) & TARGET_PAGE_MASK)
>> +#define TARGET_PAGE_ALIGN(addr) ROUND_UP((addr), TARGET_PAGE_SIZE)
>>  
>>  /* Using intptr_t ensures that qemu_*_page_mask is sign-extended even
>>   * when intptr_t is 32-bit and we are aligning a long long.
>> @@ -228,9 +228,8 @@ extern int target_page_bits;
>>  extern uintptr_t qemu_host_page_size;
>>  extern intptr_t qemu_host_page_mask;
>>  
>> -#define HOST_PAGE_ALIGN(addr) (((addr) + qemu_host_page_size - 1) & qemu_host_page_mask)
>> -#define REAL_HOST_PAGE_ALIGN(addr) (((addr) + qemu_real_host_page_size - 1) & \
>> -                                    qemu_real_host_page_mask)
>> +#define HOST_PAGE_ALIGN(addr) ROUND_UP((addr), qemu_host_page_size)
>> +#define REAL_HOST_PAGE_ALIGN(addr) ROUND_UP((addr), qemu_real_host_page_size)
>
>
>No, please.
>
>(1) The compiler does not know that qemu_*host_page_size is a power of 2, and
>will generate a real division at runtime.  The same is true for
>TARGET_PAGE_SIZE when TARGET_PAGE_BITS_VARY.
>

Confused

The definition of ROUND_UP is:

#define ROUND_UP(n, d) (((n) + (d) - 1) & -(0 ? (n) : (d)))

Why it will do division? This will be expanded to the same form as the
original code, if my understanding is correct. Would you mind telling me more?

>(2) The first hunk conflicts with an in-flight patch of mine:
>
>https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg04526.html
>
>
>r~

-- 
Wei Yang
Help you, Help me