The xor_vmx.c file is used for the RAID5 xor operations. In these functions
altivec is enabled to run the operation and then disabled.
The code uses enable_kernel_altivec() around the core of the algorithm, however
the whole file is built with -maltivec, so the compiler is within its rights to
generate altivec code anywhere. This has been seen at least once in the wild:
0:mon> di $xor_altivec_2
c0000000000b97d0 3c4c01d9 addis r2,r12,473
c0000000000b97d4 3842db30 addi r2,r2,-9424
c0000000000b97d8 7c0802a6 mflr r0
c0000000000b97dc f8010010 std r0,16(r1)
c0000000000b97e0 60000000 nop
c0000000000b97e4 7c0802a6 mflr r0
c0000000000b97e8 faa1ffa8 std r21,-88(r1)
...
c0000000000b981c f821ff41 stdu r1,-192(r1)
c0000000000b9820 7f8101ce stvx v28,r1,r0 <-- POP
c0000000000b9824 38000030 li r0,48
c0000000000b9828 7fa101ce stvx v29,r1,r0
...
c0000000000b984c 4bf6a06d bl c0000000000238b8 # enable_kernel_altivec
This patch splits the non-altivec code into xor_vmx_glue.c which calls the
altivec functions in xor_vmx.c. By compiling xor_vmx_glue.c without
-maltivec we can guarantee that altivec instruction will not be executed
outside of the enable/disable block.
Signed-off-by: Matt Brown <matthew.brown.dev@gmail.com>
[mpe: Rework change log and include disassembly]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Sparse doesn't seem to be passing -maltivec around properly, leading
to lots of errors:
.../include/altivec.h:34:2: error: Use the "-maltivec" flag to enable PowerPC AltiVec support
arch/powerpc/lib/xor_vmx.c:27:16: error: Expected ; at end of declaration
arch/powerpc/lib/xor_vmx.c:27:16: error: got signed
arch/powerpc/lib/xor_vmx.c:60:9: error: No right hand side of '*'-expression
arch/powerpc/lib/xor_vmx.c:60:9: error: Expected ; at end of statement
arch/powerpc/lib/xor_vmx.c:60:9: error: got v1_in
...
arch/powerpc/lib/xor_vmx.c:87:9: error: too many errors
Only include the altivec.h header for non-__CHECKER__ builds.
For builds with __CHECKER__, make up some stubs instead, as
suggested by Balbir. (The vector size of 16 is arbitrary.)
Suggested-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Tested-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
The enable_kernel_*() functions leave the relevant MSR bits enabled
until we exit the kernel sometime later. Create disable versions
that wrap the kernel use of FP, Altivec VSX or SPE.
While we don't want to disable it normally for performance reasons
(MSR writes are slow), it will be used for a debug boot option that
does this and catches bad uses in other areas of the kernel.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Add a VMX optimised xor, used primarily for RAID5. On a POWER7 blade
this is a decent win:
32regs : 17932.800 MB/sec
altivec : 19724.800 MB/sec
The bigger gain is when the same test is run in SMT4 mode, as it
would if there was a lot of work going on:
8regs : 8377.600 MB/sec
altivec : 15801.600 MB/sec
I tested this against an array created without the patch, and also
verified it worked as expected on a little endian kernel.
[ Fix !CONFIG_ALTIVEC build -- BenH ]
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Matt Brown