There's no need for the K_table to be made of 64-bit words. For some
reason, the original authors didn't fully reduce the values modulo the
CRC32C polynomial, and so had some 33-bit values in there. They can
all be reduced to 32 bits.
Doing that cuts the table size in half. Since the code depends on both
pclmulq and crc32, SSE 4.1 is obviously present, so we can use pmovzxdq
to fetch it in the correct format.
This adds (measured on Ivy Bridge) 1 cycle per main loop iteration
(CRC of up to 3K bytes), less than 0.2%. The hope is that the reduced
D-cache footprint will make up the loss in other code.
Two other related fixes:
* K_table is read-only, so belongs in .rodata, and
* There's no need for more than 8-byte alignment
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: George Spelvin <linux@horizon.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Occurs when CONFIG_CRYPTO_CRC32C_INTEL=y and CONFIG_CRYPTO_CRC32C_INTEL=y.
Older versions of bintuils do not support the pclmulqdq instruction. The
PCLMULQDQ gas macro is used instead.
Signed-off-by: Sandy Wu <sandyw@twitter.com>
Cc: stable@vger.kernel.org # 3.8+
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Herbert,
The following patch update the stale link to the CRC32C white paper
that was referenced.
Tim
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This patch adds the crc_pcl function that calculates CRC32C checksum using the
PCLMULQDQ instruction on processors that support this feature. This will
provide speedup over using CRC32 instruction only.
The usage of PCLMULQDQ necessitate the invocation of kernel_fpu_begin and
kernel_fpu_end and incur some overhead. So the new crc_pcl function is only
invoked for buffer size of 512 bytes or more. Larger sized
buffers will expect to see greater speedup. This feature is best used coupled
with eager_fpu which reduces the kernel_fpu_begin/end overhead. For
buffer size of 1K the speedup is around 1.6x and for buffer size greater than
4K, the speedup is around 3x compared to original implementation in crc32c-intel
module. Test was performed on Sandy Bridge based platform with constant frequency
set for cpu.
A white paper detailing the algorithm can be found here:
http://download.intel.com/design/intarch/papers/323405.pdf
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
George Spelvin