Add parity generation/rebuild using 128-bits NEON for Aarch64

This re-use the framework established for SSE2, SSSE3 and
AVX2. However, GCC is using FP registers on Aarch64, so
unlike SSE/AVX2 we can't rely on the registers being left alone
between ASM statements. So instead, the NEON code uses
C variables and GCC extended ASM syntax. Note that since
the kernel explicitly disable vector registers, they
have to be locally re-enabled explicitly.

As we use the variable's number to define the symbolic
name, and GCC won't allow duplicate symbolic names,
numbers have to be unique. Even when the code is not
going to be used (e.g. the case for 4 registers when
using the macro with only 2). Only the actually used
variables should be declared, otherwise the build
will fails in debug mode.

This requires the replacement of the XOR(X,X) syntax
by a new ZERO(X) macro, which does the same thing but
without repeating the argument. And perhaps someday
there will be a machine where there is a more efficient
way to zero a register than XOR with itself. This affects
scalar, SSE2, SSSE3 and AVX2 as they need the new macro.

It's possible to write faster implementations (different
scheduling, different unrolling, interleaving NEON and
scalar, ...) for various cores, but this one has the
advantage of fitting in the current state of the code,
and thus is likely easier to review/check/merge.

The only difference between aarch64-neon and aarch64-neonx2
is that aarch64-neonx2 unroll some functions some more.

Reviewed-by: Gvozden Neskovic <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Romain Dolbeau <[email protected]>
Closes #4801 

1 files changed, 4 insertions, 0 deletions

diff --git a/include/sys/vdev_raidz_impl.h b/include/sys/vdev_raidz_impl.h
index af09aa643..ca902f15d 100644
--- a/include/sys/vdev_raidz_impl.h
+++ b/include/sys/vdev_raidz_impl.h
@@ -141,6 +141,10 @@ extern const raidz_impl_ops_t vdev_raidz_ssse3_impl;
 #if defined(__x86_64) && defined(HAVE_AVX2)	/* only x86_64 for now */
 extern const raidz_impl_ops_t vdev_raidz_avx2_impl;
 #endif
+#if defined(__aarch64__)
+extern const raidz_impl_ops_t vdev_raidz_aarch64_neon_impl;
+extern const raidz_impl_ops_t vdev_raidz_aarch64_neonx2_impl;
+#endif
 
 /*
  * Commonly used raidz_map helpers