On 12/28/2017 05:56 PM, Grazvydas Ignotas wrote:
> zlib provides a faster slice-by-4 CRC32 implementation than the
> traditional single byte lookup one used by mesa. As most supported
> platforms now link zlib unconditionally, we can easily use it.
> For small buffers the old implementation is still used as it's faster
> with cold cache (first call), as indicated by some throughput
> benchmarking (avg MB/s, n=100, zlib 1.2.8):
>
> i5-6600K C2D E4500
> size mesa zlib mesa zlib
> 4 66 43 -35% +/- 4.8% 43 22 -49% +/- 9.6%
> 32 193 171 -11% +/- 5.8% 129 49 -61% +/- 7.2%
> 64 256 267 4% +/- 4.1% 171 63 -63% +/- 5.4%
> 128 317 389 22% +/- 5.8% 253 89 -64% +/- 4.2%
> 256 364 596 63% +/- 5.6% 304 166 -45% +/- 2.8%
> 512 401 838 108% +/- 5.3% 338 296 -12% +/- 3.1%
> 1024 420 1036 146% +/- 7.6% 375 461 23% +/- 3.7%
> 1M 443 1443 225% +/- 2.1% 403 1175 191% +/- 0.9%
> 100M 448 1452 224% +/- 0.3% 406 1214 198% +/- 0.3%
>
> With hot cache (repeated calls) zlib almost always wins on both CPUS.
> It has been verified the calculation results stay the same after this
> change.
>
> Signed-off-by: Grazvydas Ignotas <nota...@gmail.com>
> ---
> src/util/crc32.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/src/util/crc32.c b/src/util/crc32.c
> index f2e01c6..0cffa49 100644
> --- a/src/util/crc32.c
> +++ b/src/util/crc32.c
> @@ -31,12 +31,20 @@
> *
> * @author Jose Fonseca
> */
>
>
> +#ifdef HAVE_ZLIB
> +#include <zlib.h>
> +#endif
> #include "crc32.h"
>
> +/* For small buffers it's faster to avoid the library call.
> + * The optimal threshold depends on CPU characteristics, it is hoped
> + * the choice below is reasonable for typical modern CPU.
> + */
> +#define ZLIB_SIZE_THRESHOLD 64
For the actual users of this function in Mesa, is it even possible to
pass less than 64 bytes (I'm assuming that's the units)?
>
> static const uint32_t
> util_crc32_table[256] = {
> 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
> 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
> @@ -112,10 +120,15 @@ uint32_t
> util_hash_crc32(const void *data, size_t size)
> {
> const uint8_t *p = data;
> uint32_t crc = 0xffffffff;
>
> +#ifdef HAVE_ZLIB
> + if (size >= ZLIB_SIZE_THRESHOLD && (uInt)size == size)
^^^^^^^^^^^^^^^^^^
This comparison is always true (unless sizeof(uInt) != sizeof(size_t)?).
I'm not 100% sure what you're trying to accomplish here, but I think
you want 'size > 0'. I'm not familiar with this zlib function, so I
don't know what it's expectations for size are.
> + return ~crc32(0, data, size);
> +#endif
> +
> while (size--)
> crc = util_crc32_table[(crc ^ *p++) & 0xff] ^ (crc >> 8);
>
> return crc;
> }
>
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