The driver crc32c-intel match CPUs supporting X86_FEATURE_XMM4_2. On platforms with Zhaoxin CPUs supporting this X86 feature, when crc32c-intel and crc32c-generic are both registered, system will use crc32c-intel because its .cra_priority is greater than crc32c-generic. When doing lmbench3 Create and Delete file test on partitions with ext4 enabling metadata checksum, found using crc32c-generic driver could get about 20% performance gain than using the driver crc32c-intel on some Zhaoxin CPUs. Lower-level testing result is that with the same input value the generic C implementation takes fewer time than the crc32c instruction implementation on these CPUs. This case expect to use crc32c-generic driver for these CPUs to get performance gain. The presence of crc32c is enumerated by CPUID.01:ECX[SSE4.2] = 1, and these CPUs other SSE4.2 instructions is ok. Add a synthetic flag to indicates low performance CRC32C instruction implementation, set this flag in Zhaoxin CPUs specific init phase, and exclude CPUs which setting this flag from the driver crc32c-intel. https://lkml.org/lkml/2020/12/21/789 Tony W Wang-oc (3): x86/cpufeatures: Add low performance CRC32C instruction CPU feature x86/cpu: Set low performance CRC32C flag on some Zhaoxin CPUs crypto: x86/crc32c-intel Exclude low performance CRC32C instruction CPUs arch/x86/crypto/crc32c-intel_glue.c | 5 +++++ arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/kernel/cpu/centaur.c | 7 +++++++ arch/x86/kernel/cpu/cpuid-deps.c | 1 + arch/x86/kernel/cpu/zhaoxin.c | 6 ++++++ 5 files changed, 20 insertions(+) -- 2.7.4
