* [PATCH 2/3] xor: opt out of initializing MXCSR and 387 state
2026-11-11 20:56 [PATCH 0/3] lib/raid: opt out of initializing MXCSR and 387 state Eric Biggers
2026-11-11 20:56 ` [PATCH 1/3] um: Define kernel_fpu_begin_mask() Eric Biggers
@ 2026-11-11 20:56 ` Eric Biggers
2026-11-11 20:56 ` [PATCH 3/3] raid6: " Eric Biggers
2026-11-12 13:40 ` [PATCH 0/3] lib/raid: " Christoph Hellwig
3 siblings, 0 replies; 6+ messages in thread
From: Eric Biggers @ 2026-11-11 20:56 UTC (permalink / raw)
To: akpm, linux-raid
Cc: linux-crypto, x86, Christoph Hellwig, Richard Weinberger,
Anton Ivanov, Johannes Berg, Eric Biggers
The XOR code using "kernel-mode FPU" is integer code that does not use
any MMX or x87 instructions. (MMX optimized code previously existed but
was recently removed.) To the extent that float-domain instructions are
used at all, they are only moves, shuffles, and XORs, none of which
raises SIMD floating-point exceptions or depends on MXCSR.
Therefore, there's no need to initialize MXCSR or the 387 FPU state.
Opt out of this initialization by using kernel_fpu_begin_mask(0) instead
of kernel_fpu_begin(). This eliminates an 'ldmxcsr' instruction in
every kernel-mode FPU section, reducing overhead, which matters most for
short input lengths. On 32-bit kernels it also eliminates 'fninit'.
This will make the RAID code consistent with the crypto and CRC code,
which are also switching to kernel_fpu_begin_mask(0)
(https://lore.kernel.org/linux-crypto/20261105005523.84925-1-ebiggers@kernel.org/).
Another precedent for this optimization can be found in
commit a58db7ad80e8 ("netfilter: nft_set_pipapo_avx2: Skip LDMXCSR, we
don't need a valid MXCSR state").
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
lib/raid/xor/x86/xor-avx.c | 2 +-
lib/raid/xor/x86/xor-avx512.c | 2 +-
lib/raid/xor/x86/xor-sse.c | 4 ++--
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/lib/raid/xor/x86/xor-avx.c b/lib/raid/xor/x86/xor-avx.c
index 95b21e7225e8d..d4154a761b408 100644
--- a/lib/raid/xor/x86/xor-avx.c
+++ b/lib/raid/xor/x86/xor-avx.c
@@ -145,7 +145,7 @@ DO_XOR_BLOCKS(avx_inner, xor_avx_2, xor_avx_3, xor_avx_4, xor_avx_5);
static void xor_gen_avx(void *dest, void **srcs, unsigned int src_cnt,
unsigned int bytes)
{
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
xor_gen_avx_inner(dest, srcs, src_cnt, bytes);
asm volatile("vzeroupper");
kernel_fpu_end();
diff --git a/lib/raid/xor/x86/xor-avx512.c b/lib/raid/xor/x86/xor-avx512.c
index c11d83441875c..1c7ce519660e4 100644
--- a/lib/raid/xor/x86/xor-avx512.c
+++ b/lib/raid/xor/x86/xor-avx512.c
@@ -110,7 +110,7 @@ DO_XOR_BLOCKS(avx512_inner, xor_avx512_2, xor_avx512_3, xor_avx512_4,
static void xor_gen_avx512(void *dest, void **srcs, unsigned int src_cnt,
unsigned int bytes)
{
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
xor_gen_avx512_inner(dest, srcs, src_cnt, bytes);
asm volatile("vzeroupper");
kernel_fpu_end();
diff --git a/lib/raid/xor/x86/xor-sse.c b/lib/raid/xor/x86/xor-sse.c
index c6626ecae6ba5..725686c0c942f 100644
--- a/lib/raid/xor/x86/xor-sse.c
+++ b/lib/raid/xor/x86/xor-sse.c
@@ -432,7 +432,7 @@ DO_XOR_BLOCKS(sse_inner, xor_sse_2, xor_sse_3, xor_sse_4, xor_sse_5);
static void xor_gen_sse(void *dest, void **srcs, unsigned int src_cnt,
unsigned int bytes)
{
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
xor_gen_sse_inner(dest, srcs, src_cnt, bytes);
kernel_fpu_end();
}
@@ -448,7 +448,7 @@ DO_XOR_BLOCKS(sse_pf64_inner, xor_sse_2_pf64, xor_sse_3_pf64, xor_sse_4_pf64,
static void xor_gen_sse_pf64(void *dest, void **srcs, unsigned int src_cnt,
unsigned int bytes)
{
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
xor_gen_sse_pf64_inner(dest, srcs, src_cnt, bytes);
kernel_fpu_end();
}
--
2.56.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 3/3] raid6: opt out of initializing MXCSR and 387 state
2026-11-11 20:56 [PATCH 0/3] lib/raid: opt out of initializing MXCSR and 387 state Eric Biggers
2026-11-11 20:56 ` [PATCH 1/3] um: Define kernel_fpu_begin_mask() Eric Biggers
2026-11-11 20:56 ` [PATCH 2/3] xor: opt out of initializing MXCSR and 387 state Eric Biggers
@ 2026-11-11 20:56 ` Eric Biggers
2026-11-12 13:40 ` [PATCH 0/3] lib/raid: " Christoph Hellwig
3 siblings, 0 replies; 6+ messages in thread
From: Eric Biggers @ 2026-11-11 20:56 UTC (permalink / raw)
To: akpm, linux-raid
Cc: linux-crypto, x86, Christoph Hellwig, Richard Weinberger,
Anton Ivanov, Johannes Berg, Eric Biggers
The RAID6 code using "kernel-mode FPU" is integer code that does not use
any MMX or x87 instructions. (MMX optimized code previously existed but
was recently removed.) To the extent that float-domain instructions are
used at all, they are only moves, shuffles, and XORs, none of which
raises SIMD floating-point exceptions or depends on MXCSR.
Therefore, there's no need to initialize MXCSR or the 387 FPU state.
Opt out of this initialization by using kernel_fpu_begin_mask(0) instead
of kernel_fpu_begin(). This eliminates an 'ldmxcsr' instruction in
every kernel-mode FPU section, reducing overhead, which matters most for
short input lengths. On 32-bit kernels it also eliminates 'fninit'.
This will make the RAID code consistent with the crypto and CRC code,
which are also switching to kernel_fpu_begin_mask(0)
(https://lore.kernel.org/linux-crypto/20261105005523.84925-1-ebiggers@kernel.org/).
Another precedent for this optimization can be found in
commit a58db7ad80e8 ("netfilter: nft_set_pipapo_avx2: Skip LDMXCSR, we
don't need a valid MXCSR state").
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
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 ++++++------
6 files changed, 24 insertions(+), 24 deletions(-)
diff --git a/lib/raid/raid6/x86/avx2.c b/lib/raid/raid6/x86/avx2.c
index 3cc2fe7ac42c5..e09d0bd418efc 100644
--- a/lib/raid/raid6/x86/avx2.c
+++ b/lib/raid/raid6/x86/avx2.c
@@ -32,7 +32,7 @@ static void raid6_avx21_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa %0,%%ymm0" : : "m" (raid6_avx2_constants.x1d[0]));
asm volatile("vpxor %ymm3,%ymm3,%ymm3"); /* Zero temp */
@@ -82,7 +82,7 @@ static void raid6_avx21_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa %0,%%ymm0" : : "m" (raid6_avx2_constants.x1d[0]));
@@ -139,7 +139,7 @@ static void raid6_avx22_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa %0,%%ymm0" : : "m" (raid6_avx2_constants.x1d[0]));
asm volatile("vpxor %ymm1,%ymm1,%ymm1"); /* Zero temp */
@@ -192,7 +192,7 @@ static void raid6_avx22_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa %0,%%ymm0" : : "m" (raid6_avx2_constants.x1d[0]));
@@ -271,7 +271,7 @@ static void raid6_avx24_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa %0,%%ymm0" : : "m" (raid6_avx2_constants.x1d[0]));
asm volatile("vpxor %ymm1,%ymm1,%ymm1"); /* Zero temp */
@@ -353,7 +353,7 @@ static void raid6_avx24_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa %0,%%ymm0" :: "m" (raid6_avx2_constants.x1d[0]));
diff --git a/lib/raid/raid6/x86/avx512.c b/lib/raid/raid6/x86/avx512.c
index 772bfc4af6dfd..6ba5ca7df29d5 100644
--- a/lib/raid/raid6/x86/avx512.c
+++ b/lib/raid/raid6/x86/avx512.c
@@ -34,7 +34,7 @@ static void raid6_avx5121_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa64 %0,%%zmm0\n\t"
"vpxorq %%zmm1,%%zmm1,%%zmm1" /* Zero temp */
@@ -93,7 +93,7 @@ static void raid6_avx5121_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa64 %0,%%zmm0"
: : "m" (raid6_avx512_constants.x1d[0]));
@@ -161,7 +161,7 @@ static void raid6_avx5122_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa64 %0,%%zmm0\n\t"
"vpxorq %%zmm1,%%zmm1,%%zmm1" /* Zero temp */
@@ -225,7 +225,7 @@ static void raid6_avx5122_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa64 %0,%%zmm0"
: : "m" (raid6_avx512_constants.x1d[0]));
@@ -320,7 +320,7 @@ static void raid6_avx5124_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa64 %0,%%zmm0\n\t"
"vpxorq %%zmm1,%%zmm1,%%zmm1\n\t" /* Zero temp */
@@ -415,7 +415,7 @@ static void raid6_avx5124_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vmovdqa64 %0,%%zmm0"
:: "m" (raid6_avx512_constants.x1d[0]));
diff --git a/lib/raid/raid6/x86/recov_avx2.c b/lib/raid/raid6/x86/recov_avx2.c
index 820871046e305..41c050746b3dd 100644
--- a/lib/raid/raid6/x86/recov_avx2.c
+++ b/lib/raid/raid6/x86/recov_avx2.c
@@ -43,7 +43,7 @@ static void raid6_2data_recov_avx2(int disks, size_t bytes, int faila,
qmul = raid6_vgfmul[raid6_gfinv[raid6_gfexp[faila] ^
raid6_gfexp[failb]]];
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
/* ymm0 = x0f[16] */
asm volatile("vpbroadcastb %0, %%ymm7" : : "m" (x0f));
@@ -205,7 +205,7 @@ static void raid6_datap_recov_avx2(int disks, size_t bytes, int faila,
/* Now, pick the proper data tables */
qmul = raid6_vgfmul[raid6_gfinv[raid6_gfexp[faila]]];
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vpbroadcastb %0, %%ymm7" : : "m" (x0f));
diff --git a/lib/raid/raid6/x86/recov_avx512.c b/lib/raid/raid6/x86/recov_avx512.c
index 299a3f044d616..3b48822b61ac3 100644
--- a/lib/raid/raid6/x86/recov_avx512.c
+++ b/lib/raid/raid6/x86/recov_avx512.c
@@ -48,7 +48,7 @@ static void raid6_2data_recov_avx512(int disks, size_t bytes, int faila,
qmul = raid6_vgfmul[raid6_gfinv[raid6_gfexp[faila] ^
raid6_gfexp[failb]]];
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
/* zmm0 = x0f[16] */
asm volatile("vpbroadcastb %0, %%zmm7" : : "m" (x0f));
@@ -243,7 +243,7 @@ static void raid6_datap_recov_avx512(int disks, size_t bytes, int faila,
/* Now, pick the proper data tables */
qmul = raid6_vgfmul[raid6_gfinv[raid6_gfexp[faila]]];
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("vpbroadcastb %0, %%zmm7" : : "m" (x0f));
diff --git a/lib/raid/raid6/x86/recov_ssse3.c b/lib/raid/raid6/x86/recov_ssse3.c
index 700bd2c865ece..5540944945d57 100644
--- a/lib/raid/raid6/x86/recov_ssse3.c
+++ b/lib/raid/raid6/x86/recov_ssse3.c
@@ -44,7 +44,7 @@ static void raid6_2data_recov_ssse3(int disks, size_t bytes, int faila,
qmul = raid6_vgfmul[raid6_gfinv[raid6_gfexp[faila] ^
raid6_gfexp[failb]]];
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0,%%xmm7" : : "m" (x0f[0]));
@@ -210,7 +210,7 @@ static void raid6_datap_recov_ssse3(int disks, size_t bytes, int faila,
/* Now, pick the proper data tables */
qmul = raid6_vgfmul[raid6_gfinv[raid6_gfexp[faila]]];
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0, %%xmm7" : : "m" (x0f[0]));
diff --git a/lib/raid/raid6/x86/sse2.c b/lib/raid/raid6/x86/sse2.c
index 43b09ce58270a..2bbb288c244fc 100644
--- a/lib/raid/raid6/x86/sse2.c
+++ b/lib/raid/raid6/x86/sse2.c
@@ -28,7 +28,7 @@ static void raid6_sse21_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0,%%xmm0" : : "m" (raid6_sse_constants.x1d[0]));
asm volatile("pxor %xmm5,%xmm5"); /* Zero temp */
@@ -80,7 +80,7 @@ static void raid6_sse21_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0,%%xmm0" : : "m" (raid6_sse_constants.x1d[0]));
@@ -136,7 +136,7 @@ static void raid6_sse22_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0,%%xmm0" : : "m" (raid6_sse_constants.x1d[0]));
asm volatile("pxor %xmm5,%xmm5"); /* Zero temp */
@@ -189,7 +189,7 @@ static void raid6_sse22_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0,%%xmm0" : : "m" (raid6_sse_constants.x1d[0]));
@@ -266,7 +266,7 @@ static void raid6_sse24_gen_syndrome(int disks, size_t bytes, void **ptrs)
p = dptr[z0+1]; /* XOR parity */
q = dptr[z0+2]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0,%%xmm0" :: "m" (raid6_sse_constants.x1d[0]));
asm volatile("pxor %xmm2,%xmm2"); /* P[0] */
@@ -353,7 +353,7 @@ static void raid6_sse24_xor_syndrome(int disks, int start, int stop,
p = dptr[disks-2]; /* XOR parity */
q = dptr[disks-1]; /* RS syndrome */
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(0);
asm volatile("movdqa %0,%%xmm0" :: "m" (raid6_sse_constants.x1d[0]));
--
2.56.1
^ permalink raw reply related [flat|nested] 6+ messages in thread