lib/raid6/altivec: Add vpermxor implementation for raid6 Q syndrome

This patch uses the vpermxor instruction to optimise the raid6 Q
syndrome. This instruction was made available with POWER8, ISA version
2.07. It allows for both vperm and vxor instructions to be done in a
single instruction. This has been tested for correctness on a ppc64le
vm with a basic RAID6 setup containing 5 drives.

The performance benchmarks are from the raid6test in the
/lib/raid6/test directory. These results are from an IBM Firestone
machine with ppc64le architecture. The benchmark results show a 35%
speed increase over the best existing algorithm for powerpc (altivec).
The raid6test has also been run on a big-endian ppc64 vm to ensure it
also works for big-endian architectures.

Performance benchmarks:
  raid6: altivecx4 gen() 18773 MB/s
  raid6: altivecx8 gen() 19438 MB/s

  raid6: vpermxor4 gen() 25112 MB/s
  raid6: vpermxor8 gen() 26279 MB/s

Signed-off-by: Matt Brown <matthew.brown.dev@gmail.com>
Reviewed-by: Daniel Axtens <dja@axtens.net>
[mpe: Add VPERMXOR macro so we can build with old binutils]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 105 insertions, 0 deletions

diff --git a/lib/raid6/vpermxor.uc b/lib/raid6/vpermxor.uc
new file mode 100644
index 000000000000..10475dc423c1
--- /dev/null
+++ b/lib/raid6/vpermxor.uc
@@ -0,0 +1,105 @@
+/*
+ * Copyright 2017, Matt Brown, IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ * vpermxor$#.c
+ *
+ * Based on H. Peter Anvin's paper - The mathematics of RAID-6
+ *
+ * $#-way unrolled portable integer math RAID-6 instruction set
+ * This file is postprocessed using unroll.awk
+ *
+ * vpermxor$#.c makes use of the vpermxor instruction to optimise the RAID6 Q
+ * syndrome calculations.
+ * This can be run on systems which have both Altivec and vpermxor instruction.
+ *
+ * This instruction was introduced in POWER8 - ISA v2.07.
+ */
+
+#include <linux/raid/pq.h>
+#ifdef CONFIG_ALTIVEC
+
+#include <altivec.h>
+#ifdef __KERNEL__
+#include <asm/cputable.h>
+#include <asm/ppc-opcode.h>
+#include <asm/switch_to.h>
+#endif
+
+typedef vector unsigned char unative_t;
+#define NSIZE sizeof(unative_t)
+
+static const vector unsigned char gf_low = {0x1e, 0x1c, 0x1a, 0x18, 0x16, 0x14,
+					    0x12, 0x10, 0x0e, 0x0c, 0x0a, 0x08,
+					    0x06, 0x04, 0x02,0x00};
+static const vector unsigned char gf_high = {0xfd, 0xdd, 0xbd, 0x9d, 0x7d, 0x5d,
+					     0x3d, 0x1d, 0xe0, 0xc0, 0xa0, 0x80,
+					     0x60, 0x40, 0x20, 0x00};
+
+static void noinline raid6_vpermxor$#_gen_syndrome_real(int disks, size_t bytes,
+							void **ptrs)
+{
+	u8 **dptr = (u8 **)ptrs;
+	u8 *p, *q;
+	int d, z, z0;
+	unative_t wp$$, wq$$, wd$$;
+
+	z0 = disks - 3;		/* Highest data disk */
+	p = dptr[z0+1];		/* XOR parity */
+	q = dptr[z0+2];		/* RS syndrome */
+
+	for (d = 0; d < bytes; d += NSIZE*$#) {
+		wp$$ = wq$$ = *(unative_t *)&dptr[z0][d+$$*NSIZE];
+
+		for (z = z0-1; z>=0; z--) {
+			wd$$ = *(unative_t *)&dptr[z][d+$$*NSIZE];
+			/* P syndrome */
+			wp$$ = vec_xor(wp$$, wd$$);
+
+			/* Q syndrome */
+			asm(VPERMXOR(%0,%1,%2,%3):"=v"(wq$$):"v"(gf_high), "v"(gf_low), "v"(wq$$));
+			wq$$ = vec_xor(wq$$, wd$$);
+		}
+		*(unative_t *)&p[d+NSIZE*$$] = wp$$;
+		*(unative_t *)&q[d+NSIZE*$$] = wq$$;
+	}
+}
+
+static void raid6_vpermxor$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
+{
+	preempt_disable();
+	enable_kernel_altivec();
+
+	raid6_vpermxor$#_gen_syndrome_real(disks, bytes, ptrs);
+
+	disable_kernel_altivec();
+	preempt_enable();
+}
+
+int raid6_have_altivec_vpermxor(void);
+#if $# == 1
+int raid6_have_altivec_vpermxor(void)
+{
+	/* Check if arch has both altivec and the vpermxor instructions */
+# ifdef __KERNEL__
+	return (cpu_has_feature(CPU_FTR_ALTIVEC_COMP) &&
+		cpu_has_feature(CPU_FTR_ARCH_207S));
+# else
+	return 1;
+#endif
+
+}
+#endif
+
+const struct raid6_calls raid6_vpermxor$# = {
+	raid6_vpermxor$#_gen_syndrome,
+	NULL,
+	raid6_have_altivec_vpermxor,
+	"vpermxor$#",
+	0
+};
+#endif