md/raid6: fix algorithm choice under larger PAGE_SIZE

There are several algorithms available for raid6 to generate xor and syndrome
parity, including basic int1, int2 ... int32 and SIMD optimized implementation
like sse and neon.  To test and choose the best algorithms at the initial
stage, we need provide enough disk data to feed the algorithms. However, the
disk number we provided depends on page size and gfmul table, seeing bellow:

    const int disks = (65536/PAGE_SIZE) + 2;

So when come to 64K PAGE_SIZE, there is only one data disk plus 2 parity disk,
as a result the chosed algorithm is not reliable. For example, on my arm64
machine with 64K page enabled, it will choose intx32 as the best one, although
the NEON implementation is better.

This patch tries to fix the problem by defining a constant raid6 disk number to
supporting arbitrary page size.
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Zhengyuan Liu <liuzhengyuan@kylinos.cn>
Signed-off-by: Song Liu <songliubraving@fb.com>

include/linux/raid/pq.h

@@ -28,6 +28,7 @@ extern const char raid6_empty_zero_page[PAGE_SIZE];
 #include <errno.h>
 #include <inttypes.h>
 #include <stddef.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/time.h>
 #include <sys/types.h>
@@ -43,6 +44,9 @@ typedef uint64_t u64;
 #ifndef PAGE_SIZE
 # define PAGE_SIZE 4096
 #endif
+#ifndef PAGE_SHIFT
+# define PAGE_SHIFT 12
+#endif
 extern const char raid6_empty_zero_page[PAGE_SIZE];
 
 #define __init

lib/raid6/algos.c

@@ -124,6 +124,9 @@ const struct raid6_recov_calls *const raid6_recov_algos[] = {
 #define time_before(x, y) ((x) < (y))
 #endif
 
+#define RAID6_TEST_DISKS	8
+#define RAID6_TEST_DISKS_ORDER	3
+
 static inline const struct raid6_recov_calls *raid6_choose_recov(void)
 {
 	const struct raid6_recov_calls *const *algo;
@@ -146,7 +149,7 @@ static inline const struct raid6_recov_calls *raid6_choose_recov(void)
 }
 
 static inline const struct raid6_calls *raid6_choose_gen(
-	void *(*const dptrs)[(65536/PAGE_SIZE)+2], const int disks)
+	void *(*const dptrs)[RAID6_TEST_DISKS], const int disks)
 {
 	unsigned long perf, bestgenperf, bestxorperf, j0, j1;
 	int start = (disks>>1)-1, stop = disks-3;	/* work on the second half of the disks */
@@ -181,7 +184,8 @@ static inline const struct raid6_calls *raid6_choose_gen(
 				best = *algo;
 			}
 			pr_info("raid6: %-8s gen() %5ld MB/s\n", (*algo)->name,
-			       (perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
+				(perf * HZ * (disks-2)) >>
+				(20 - PAGE_SHIFT + RAID6_TIME_JIFFIES_LG2));
 
 			if (!(*algo)->xor_syndrome)
 				continue;
@@ -204,17 +208,24 @@ static inline const struct raid6_calls *raid6_choose_gen(
 				bestxorperf = perf;
 
 			pr_info("raid6: %-8s xor() %5ld MB/s\n", (*algo)->name,
-				(perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2+1));
+				(perf * HZ * (disks-2)) >>
+				(20 - PAGE_SHIFT + RAID6_TIME_JIFFIES_LG2 + 1));
 		}
 	}
 
 	if (best) {
-		pr_info("raid6: using algorithm %s gen() %ld MB/s\n",
-		       best->name,
-		       (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));
+		if (IS_ENABLED(CONFIG_RAID6_PQ_BENCHMARK)) {
+			pr_info("raid6: using algorithm %s gen() %ld MB/s\n",
+				best->name,
+				(bestgenperf * HZ * (disks-2)) >>
+				(20 - PAGE_SHIFT+RAID6_TIME_JIFFIES_LG2));
+			if (best->xor_syndrome)
+				pr_info("raid6: .... xor() %ld MB/s, rmw enabled\n",
+					(bestxorperf * HZ * (disks-2)) >>
+					(20 - PAGE_SHIFT + RAID6_TIME_JIFFIES_LG2 + 1));
+		} else
+			pr_info("raid6: skip pq benchmark and using algorithm %s\n",
+				best->name);
 		raid6_call = *best;
 	} else
 		pr_err("raid6: Yikes!  No algorithm found!\n");
@@ -228,27 +239,33 @@ static inline const struct raid6_calls *raid6_choose_gen(
 
 int __init raid6_select_algo(void)
 {
-	const int disks = (65536/PAGE_SIZE)+2;
+	const int disks = RAID6_TEST_DISKS;
 
 	const struct raid6_calls *gen_best;
 	const struct raid6_recov_calls *rec_best;
-	char *syndromes;
-	void *dptrs[(65536/PAGE_SIZE)+2];
-	int i;
-
-	for (i = 0; i < disks-2; i++)
-		dptrs[i] = ((char *)raid6_gfmul) + PAGE_SIZE*i;
-
-	/* Normal code - use a 2-page allocation to avoid D$ conflict */
-	syndromes = (void *) __get_free_pages(GFP_KERNEL, 1);
+	char *disk_ptr, *p;
+	void *dptrs[RAID6_TEST_DISKS];
+	int i, cycle;
 
-	if (!syndromes) {
+	/* prepare the buffer and fill it circularly with gfmul table */
+	disk_ptr = (char *)__get_free_pages(GFP_KERNEL, RAID6_TEST_DISKS_ORDER);
+	if (!disk_ptr) {
 		pr_err("raid6: Yikes!  No memory available.\n");
 		return -ENOMEM;
 	}
 
-	dptrs[disks-2] = syndromes;
-	dptrs[disks-1] = syndromes + PAGE_SIZE;
+	p = disk_ptr;
+	for (i = 0; i < disks; i++)
+		dptrs[i] = p + PAGE_SIZE * i;
+
+	cycle = ((disks - 2) * PAGE_SIZE) / 65536;
+	for (i = 0; i < cycle; i++) {
+		memcpy(p, raid6_gfmul, 65536);
+		p += 65536;
+	}
+
+	if ((disks - 2) * PAGE_SIZE % 65536)
+		memcpy(p, raid6_gfmul, (disks - 2) * PAGE_SIZE % 65536);
 
 	/* select raid gen_syndrome function */
 	gen_best = raid6_choose_gen(&dptrs, disks);
@@ -256,7 +273,7 @@ int __init raid6_select_algo(void)
 	/* select raid recover functions */
 	rec_best = raid6_choose_recov();
 
-	free_pages((unsigned long)syndromes, 1);
+	free_pages((unsigned long)disk_ptr, RAID6_TEST_DISKS_ORDER);
 
 	return gen_best && rec_best ? 0 : -EINVAL;
 }