diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c
index dbef231..975c6e0 100644
--- a/lib/raid6/algos.c
+++ b/lib/raid6/algos.c
@@ -131,11 +131,12 @@
 static inline const struct raid6_calls *raid6_choose_gen(
 	void *(*const dptrs)[(65536/PAGE_SIZE)+2], const int disks)
 {
-	unsigned long perf, bestperf, j0, j1;
+	unsigned long perf, bestgenperf, bestxorperf, j0, j1;
+	int start = (disks>>1)-1, stop = disks-3;	/* work on the second half of the disks */
 	const struct raid6_calls *const *algo;
 	const struct raid6_calls *best;
 
-	for (bestperf = 0, best = NULL, algo = raid6_algos; *algo; algo++) {
+	for (bestgenperf = 0, bestxorperf = 0, best = NULL, algo = raid6_algos; *algo; algo++) {
 		if (!best || (*algo)->prefer >= best->prefer) {
 			if ((*algo)->valid && !(*algo)->valid())
 				continue;
@@ -153,19 +154,45 @@
 			}
 			preempt_enable();
 
-			if (perf > bestperf) {
-				bestperf = perf;
+			if (perf > bestgenperf) {
+				bestgenperf = perf;
 				best = *algo;
 			}
-			pr_info("raid6: %-8s %5ld MB/s\n", (*algo)->name,
+			pr_info("raid6: %-8s gen() %5ld MB/s\n", (*algo)->name,
 			       (perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
+
+			if (!(*algo)->xor_syndrome)
+				continue;
+
+			perf = 0;
+
+			preempt_disable();
+			j0 = jiffies;
+			while ((j1 = jiffies) == j0)
+				cpu_relax();
+			while (time_before(jiffies,
+					    j1 + (1<<RAID6_TIME_JIFFIES_LG2))) {
+				(*algo)->xor_syndrome(disks, start, stop,
+						      PAGE_SIZE, *dptrs);
+				perf++;
+			}
+			preempt_enable();
+
+			if (best == *algo)
+				bestxorperf = perf;
+
+			pr_info("raid6: %-8s xor() %5ld MB/s\n", (*algo)->name,
+				(perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2+1));
 		}
 	}
 
 	if (best) {
-		pr_info("raid6: using algorithm %s (%ld MB/s)\n",
+		pr_info("raid6: using algorithm %s gen() %ld MB/s\n",
 		       best->name,
-		       (bestperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
+		       (bestgenperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
+		if (best->xor_syndrome)
+			pr_info("raid6: .... xor() %ld MB/s, rmw enabled\n",
+			       (bestxorperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2+1));
 		raid6_call = *best;
 	} else
 		pr_err("raid6: Yikes!  No algorithm found!\n");
diff --git a/lib/raid6/altivec.uc b/lib/raid6/altivec.uc
index 7cc12b5..bec27fc 100644
--- a/lib/raid6/altivec.uc
+++ b/lib/raid6/altivec.uc
@@ -119,6 +119,7 @@
 
 const struct raid6_calls raid6_altivec$# = {
 	raid6_altivec$#_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_altivec,
 	"altivecx$#",
 	0
diff --git a/lib/raid6/avx2.c b/lib/raid6/avx2.c
index bc3b1dd..7673400 100644
--- a/lib/raid6/avx2.c
+++ b/lib/raid6/avx2.c
@@ -89,6 +89,7 @@
 
 const struct raid6_calls raid6_avx2x1 = {
 	raid6_avx21_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_avx2,
 	"avx2x1",
 	1			/* Has cache hints */
@@ -150,6 +151,7 @@
 
 const struct raid6_calls raid6_avx2x2 = {
 	raid6_avx22_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_avx2,
 	"avx2x2",
 	1			/* Has cache hints */
@@ -242,6 +244,7 @@
 
 const struct raid6_calls raid6_avx2x4 = {
 	raid6_avx24_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_avx2,
 	"avx2x4",
 	1			/* Has cache hints */
diff --git a/lib/raid6/int.uc b/lib/raid6/int.uc
index 5b50f8d..5ca60be 100644
--- a/lib/raid6/int.uc
+++ b/lib/raid6/int.uc
@@ -109,7 +109,8 @@
 
 const struct raid6_calls raid6_intx$# = {
 	raid6_int$#_gen_syndrome,
-	NULL,		/* always valid */
+	NULL,			/* XOR not yet implemented */
+	NULL,			/* always valid */
 	"int" NSTRING "x$#",
 	0
 };
diff --git a/lib/raid6/mmx.c b/lib/raid6/mmx.c
index 590c71c..b3b0e1f 100644
--- a/lib/raid6/mmx.c
+++ b/lib/raid6/mmx.c
@@ -76,6 +76,7 @@
 
 const struct raid6_calls raid6_mmxx1 = {
 	raid6_mmx1_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_mmx,
 	"mmxx1",
 	0
@@ -134,6 +135,7 @@
 
 const struct raid6_calls raid6_mmxx2 = {
 	raid6_mmx2_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_mmx,
 	"mmxx2",
 	0
diff --git a/lib/raid6/neon.c b/lib/raid6/neon.c
index 36ad470..d9ad6ee 100644
--- a/lib/raid6/neon.c
+++ b/lib/raid6/neon.c
@@ -42,6 +42,7 @@
 	}								\
 	struct raid6_calls const raid6_neonx ## _n = {			\
 		raid6_neon ## _n ## _gen_syndrome,			\
+		NULL,		/* XOR not yet implemented */		\
 		raid6_have_neon,					\
 		"neonx" #_n,						\
 		0							\
diff --git a/lib/raid6/sse1.c b/lib/raid6/sse1.c
index f762971..9025b8c 100644
--- a/lib/raid6/sse1.c
+++ b/lib/raid6/sse1.c
@@ -92,6 +92,7 @@
 
 const struct raid6_calls raid6_sse1x1 = {
 	raid6_sse11_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_sse1_or_mmxext,
 	"sse1x1",
 	1			/* Has cache hints */
@@ -154,6 +155,7 @@
 
 const struct raid6_calls raid6_sse1x2 = {
 	raid6_sse12_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_sse1_or_mmxext,
 	"sse1x2",
 	1			/* Has cache hints */
diff --git a/lib/raid6/sse2.c b/lib/raid6/sse2.c
index 85b82c8..31acd59 100644
--- a/lib/raid6/sse2.c
+++ b/lib/raid6/sse2.c
@@ -90,6 +90,7 @@
 
 const struct raid6_calls raid6_sse2x1 = {
 	raid6_sse21_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_sse2,
 	"sse2x1",
 	1			/* Has cache hints */
@@ -152,6 +153,7 @@
 
 const struct raid6_calls raid6_sse2x2 = {
 	raid6_sse22_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_sse2,
 	"sse2x2",
 	1			/* Has cache hints */
@@ -250,6 +252,7 @@
 
 const struct raid6_calls raid6_sse2x4 = {
 	raid6_sse24_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	raid6_have_sse2,
 	"sse2x4",
 	1			/* Has cache hints */
diff --git a/lib/raid6/tilegx.uc b/lib/raid6/tilegx.uc
index e7c2945..2dd291a 100644
--- a/lib/raid6/tilegx.uc
+++ b/lib/raid6/tilegx.uc
@@ -80,6 +80,7 @@
 
 const struct raid6_calls raid6_tilegx$# = {
 	raid6_tilegx$#_gen_syndrome,
+	NULL,			/* XOR not yet implemented */
 	NULL,
 	"tilegx$#",
 	0