Re: define pg_structiszero(addr, s, r)

Em sáb., 16 de nov. de 2024 às 11:40, Ranier Vilela <ranier(dot)vf(at)gmail(dot)com>
escreveu:

>
> Em sex., 15 de nov. de 2024 às 11:43, Bertrand Drouvot <
> bertranddrouvot(dot)pg(at)gmail(dot)com> escreveu:
>
>> Hi,
>>
>> On Fri, Nov 15, 2024 at 09:54:33AM -0300, Ranier Vilela wrote:
>> > There is a tiny typo with V13.
>> > + /* "len" in the [sizeof(size_t) * 8, inf] range */
>>
>> I think "[sizeof(size_t) * 8, inf[ range" is correct. Infinity can not be
>> included
>> into a interval.
>>
>> Thinking about it, actually, "[sizeof(size_t) * 8, inf)" (note the ')' at
>> the end)
>> might be the proper notation from a mathematical point of view.
>>
> Thanks for clarifying.
>
>
>>
>> > But, I'm not sure if I'm still doing something wrong.
>> > If so, forgive me for the noise.
>> >
>> > Of course I expected "not is_allzeros".
>>
>> That's the test case which is "wrong" (not the function):
>>
>> "
>> size_t pagebytes[BLCKSZ] = {0};
>> volatile bool result;
>>
>> pagebytes[BLCKSZ-2] = 1;
>>
>> result = pg_memory_is_all_zeros_v12(pagebytes, BLCKSZ);
>> "
>>
>> The pagebytes is an array of size_t (8 bytes each), so the actual array
>> size
>> is 8192 * 8 = 65536 bytes.
>>
>> So, pagebytes[BLCKSZ-2] = 1, sets byte 65528 ((8192-2)*8) to 1.
>>
>> But the function is checking up to BLCKSZ bytes (8192), so the results you
>> observed (which are correct).
>>
> Thanks for pointing out my mistake.
>
>
>>
>> > Anyway, I made another attempt to optimize a bit more, I don't know if
>> it's
>> > safe though.
>>
>> There is an issue in your v14, it calls:
>>
>> "
>> return pg_memory_is_all_zeros_simd(ptr, ptr + len);
>> "
>>
>> but you defined it that way:
>>
>> "
>> static inline bool
>> pg_memory_is_all_zeros_simd(const size_t *p, const size_t * end)
>>
>> "
>>
>> while that should be:
>>
>> "
>> static inline bool
>> pg_memory_is_all_zeros_simd(const void *p, const void *end)
>>
> What I'm trying here, obviously, is a hack.
> If it works, and the compiler accepts it, it's ok for me.
>
>
>> "
>>
>> Doing so, I do not observe any improvments with v14.
>>
> So.
> Again new results from v4_allzeros_small.c attached:
> Linux Ubuntu 22.04
> gcc 13 64 bits
>
> With BLCKSZ 32
> gcc -march=native -O2 v4_allzeros_small.c -o v4_allzeros_small ;
> ./v4_allzeros_small
> byte per byte: done in 44092 nanoseconds
> size_t: done in 13456 nanoseconds (3.27675 times faster than byte per byte)
> SIMD v10: done in 14249 nanoseconds (3.09439 times faster than byte per
> byte)
> SIMD v11: done in 32516 nanoseconds (1.35601 times faster than byte per
> byte)
> SIMD v12: done in 14973 nanoseconds (2.94477 times faster than byte per
> byte)
> SIMD v14: done in 13101 nanoseconds (3.36554 times faster than byte per
> byte)
>
> With BLCKSZ 63
> gcc -march=native -O2 v4_allzeros_small.c -o v4_allzeros_small ;
> ./v4_allzeros_small
> byte per byte: done in 67656 nanoseconds
> size_t: done in 25768 nanoseconds (2.62558 times faster than byte per byte)
> SIMD v10: done in 21446 nanoseconds (3.15471 times faster than byte per
> byte)
> SIMD v11: done in 56887 nanoseconds (1.18931 times faster than byte per
> byte)
> SIMD v12: done in 22863 nanoseconds (2.95919 times faster than byte per
> byte)
> SIMD v14: done in 21273 nanoseconds (3.18037 times faster than byte per
> byte)
>
> With BLCKSZ 256
> gcc -march=native -O2 v4_allzeros_small.c -o v4_allzeros_small ;
> ./v4_allzeros_small
> byte per byte: done in 220064 nanoseconds
> size_t: done in 45886 nanoseconds (4.79589 times faster than byte per byte)
> SIMD v10: done in 12032 nanoseconds (18.2899 times faster than byte per
> byte)
> SIMD v11: done in 11965 nanoseconds (18.3923 times faster than byte per
> byte)
> SIMD v12: done in 12041 nanoseconds (18.2762 times faster than byte per
> byte)
> SIMD v14: done in 12575 nanoseconds (17.5001 times faster than byte per
> byte)
>
> With BLCKSZ 8192
> gcc -march=native -O2 v4_allzeros_small.c -o v4_allzeros_small ;
> ./v4_allzeros_small
> byte per byte: done in 10365876 nanoseconds
> size_t: done in 827654 nanoseconds (12.5244 times faster than byte per
> byte)
> SIMD v10: done in 347755 nanoseconds (29.808 times faster than byte per
> byte)
> SIMD v11: done in 342813 nanoseconds (30.2377 times faster than byte per
> byte)
> SIMD v12: done in 341124 nanoseconds (30.3874 times faster than byte per
> byte)
> SIMD v14: done in 50646 nanoseconds (204.673 times faster than byte per
> byte)
>
> Results with v4_allzeros_check.c attached:
> gcc -march=native -O2 v4_allzeros_check.c -o v4_allzeros_check ;
> ./v4_allzeros_check
> sizeof(pagebytes)=32
> byte per byte: is_allzeros
> size_t: is_allzeros
> SIMD v10: is_allzeros
> SIMD v11: is_allzeros
> SIMD v12: is_allzeros
> SIMD v14: is_allzeros
>
> gcc -march=native -O2 v4_allzeros_check.c -o v4_allzeros_check ;
> ./v4_allzeros_check
> sizeof(pagebytes)=63
> byte per byte: is_allzeros
> size_t: is_allzeros
> SIMD v10: is_allzeros
> SIMD v11: is_allzeros
> SIMD v12: is_allzeros
> SIMD v14: is_allzeros
>
> gcc -march=native -O2 v4_allzeros_check.c -o v4_allzeros_check ;
> ./v4_allzeros_check
> sizeof(pagebytes)=256
> byte per byte: is_allzeros
> size_t: is_allzeros
> SIMD v10: is_allzeros
> SIMD v11: is_allzeros
> SIMD v12: is_allzeros
> p01=(0x7ffedb8ac430)
> end=(0x7ffedb8ac530)
> p02=(0x7ffedb8ac530)
> SIMD v14: is_allzeros
>
> gcc -march=native -O2 v4_allzeros_check.c -o v4_allzeros_check ;
> ./v4_allzeros_check
> sizeof(pagebytes)=8192
> byte per byte: is_allzeros
> size_t: is_allzeros
> SIMD v10: is_allzeros
> SIMD v11: is_allzeros
> SIMD v12: is_allzeros
> p01=(0x7ffd8864c200)
> end=(0x7ffd8864e200)
> p02=(0x7ffd8864e200)
> SIMD v14: is_allzeros
>
> If this hack is safe and correct, I think that 204 times faster,
> it is very good, for a block size 8192.
>
> That said,
> V13 is fine as is.
> LGTM.
>
Now with files attached.

best regards,
Ranier Vilela