[PATCH 0/3] lib/raid: opt out of initializing MXCSR and 387 state

[Eric Biggers <ebiggers@kernel.org>]

This series slightly reduces the overhead of the x86 kernel-mode "FPU"
sections in the RAID code by using kernel_fpu_begin_mask(0) instead of
kernel_fpu_begin(), thus opting out of the 'ldmxcsr' (and on 32-bit
kernels, also 'fninit').  MXCSR is irrelevant for integer code.

This mirrors similar optimizations for the crypto and CRC code
(https://lore.kernel.org/linux-crypto/20261105005523.84925-1-ebiggers@kernel.org/).
It's more important there than in the RAID code, since short lengths are
common in the x86-optimized crypto and CRC functions.  However, I think
it's worth updating the RAID code too for consistency.

Unlike the crypto and CRC code, the RAID code is built for user-mode
Linux.  Therefore, as a prerequisite for this change, patch 1 also
defines a stub for kernel_fpu_begin_mask() on user-mode Linux.

This series is targeting mm/mm-nonmm-unstable.

Eric Biggers (3):
  um: Define kernel_fpu_begin_mask()
  xor: opt out of initializing MXCSR and 387 state
  raid6: opt out of initializing MXCSR and 387 state

 arch/um/include/asm/fpu/api.h     |  1 +
 lib/raid/raid6/x86/avx2.c         | 12 ++++++------
 lib/raid/raid6/x86/avx512.c       | 12 ++++++------
 lib/raid/raid6/x86/recov_avx2.c   |  4 ++--
 lib/raid/raid6/x86/recov_avx512.c |  4 ++--
 lib/raid/raid6/x86/recov_ssse3.c  |  4 ++--
 lib/raid/raid6/x86/sse2.c         | 12 ++++++------
 lib/raid/xor/x86/xor-avx.c        |  2 +-
 lib/raid/xor/x86/xor-avx512.c     |  2 +-
 lib/raid/xor/x86/xor-sse.c        |  4 ++--
 10 files changed, 29 insertions(+), 28 deletions(-)


base-commit: d0ad02b9d5dd7ae551f450cfd233f3e28bbf59d3
-- 
2.56.1