Implement new reading algorithm, which will use parity component for reading

as well, even if device is in complete state.
I observe 40% of speed-up with this option for random read operations,
but slowdown for sequential reads.
Basically, without this option reading from a RAID3 device built from 5
components (c0-c4) looks like this:

	Request no.	Used components
	1		c0+c1+c2+c3
	2		c0+c1+c2+c3
	3		c0+c1+c2+c3

With the new feature:

	Request no.	Used components
	1		c0+c1+c2+c3
	2		(c1^c2^c3^c4)+c1+c2+c3
	3		c0+(c0^c2^c3^c4)+c2+c3
	4		c0+c1+(c0^c1^c3^c4)+c3
	5		c0+c1+c2+(c0^c1^c2^c4)
	6		c0+c1+c2+c3
	[...]

2 files changed, 30 insertions, 9 deletions

diff --git a/sbin/geom/class/raid3/geom_raid3.c b/sbin/geom/class/raid3/geom_raid3.c
index 55b1056..c7120ed 100644
--- a/sbin/geom/class/raid3/geom_raid3.c
+++ b/sbin/geom/class/raid3/geom_raid3.c
@@ -58,6 +58,8 @@ struct g_command class_commands[] = {
 		{ 'd', "dynamic", NULL, G_TYPE_NONE },
 		{ 'h', "hardcode", NULL, G_TYPE_NONE },
 		{ 'n', "noautosync", NULL, G_TYPE_NONE },
+		{ 'r', "round_robin", NULL, G_TYPE_NONE },
+		{ 'R', "noround_robin", NULL, G_TYPE_NONE },
 		G_OPT_SENTINEL
 	    }
 	},
@@ -73,6 +75,7 @@ struct g_command class_commands[] = {
 	    {
 		{ 'h', "hardcode", NULL, G_TYPE_NONE },
 		{ 'n', "noautosync", NULL, G_TYPE_NONE },
+		{ 'r', "round_robin", NULL, G_TYPE_NONE },
 		G_OPT_SENTINEL
 	    }
 	},
@@ -99,10 +102,10 @@ void
 usage(const char *comm)
 {
 	fprintf(stderr,
-	    "usage: %s label [-hnv] name prov prov prov [prov [...]]\n"
+	    "usage: %s label [-hnrv] name prov prov prov [prov [...]]\n"
 	    "       %s clear [-v] prov [prov [...]]\n"
 	    "       %s dump prov [prov [...]]\n"
-	    "       %s configure [-adhnv] name\n"
+	    "       %s configure [-adhnrRv] name\n"
 	    "       %s rebuild [-v] name prov\n"
 	    "       %s insert [-hv] <-n number> name prov\n"
 	    "       %s remove [-v] <-n number> name\n"
@@ -141,7 +144,8 @@ raid3_label(struct gctl_req *req)
 	u_char sector[512];
 	const char *str;
 	char param[16];
-	int *hardcode, *nargs, *noautosync, error, i;
+	int *hardcode, *nargs, *noautosync, *round_robin;
+	int error, i;
 	unsigned sectorsize;
 	off_t mediasize;
 
@@ -184,6 +188,13 @@ raid3_label(struct gctl_req *req)
 	}
 	if (*noautosync)
 		md.md_mflags |= G_RAID3_DEVICE_FLAG_NOAUTOSYNC;
+	round_robin = gctl_get_paraml(req, "round_robin", sizeof(*round_robin));
+	if (round_robin == NULL) {
+		gctl_error(req, "No '%s' argument.", "round_robin");
+		return;
+	}
+	if (*round_robin)
+		md.md_mflags |= G_RAID3_DEVICE_FLAG_ROUND_ROBIN;
 	hardcode = gctl_get_paraml(req, "hardcode", sizeof(*hardcode));
 	if (hardcode == NULL) {
 		gctl_error(req, "No '%s' argument.", "hardcode");
diff --git a/sbin/geom/class/raid3/graid3.8 b/sbin/geom/class/raid3/graid3.8
index f38732d..713f979 100644
--- a/sbin/geom/class/raid3/graid3.8
+++ b/sbin/geom/class/raid3/graid3.8
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd Aug 18, 2004
+.Dd Aug 20, 2004
 .Dt GRAID3 8
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Sh SYNOPSIS
 .Nm
 .Cm label
-.Op Fl hnv
+.Op Fl hnrv
 .Ar name
 .Ar prov
 .Ar prov
@@ -46,7 +46,7 @@
 .Op Ar prov Op Ar ...
 .Nm
 .Cm configure
-.Op Fl adhnv
+.Op Fl adhnrRv
 .Ar name
 .Nm
 .Cm rebuild
@@ -106,6 +106,12 @@ Additional options include:
 Hardcode providers' names in metadata.
 .It Fl n
 Turn off autosynchronization of stale components.
+.It Fl r
+Use parity component for reading in round-robin fashion.
+Without this option parity component is not used at all for reading operations
+when device is in complete state.
+With this option specified random I/O read operations are even 40% faster,
+but sequential reads are slower.
 .El
 .It Cm clear
 Clear metadata on the given providers.
@@ -122,6 +128,10 @@ Do not hardcode providers' names in metadata.
 Hardcode providers' names in metadata.
 .It Fl n
 Turn off autosynchronization of stale components.
+.It Fl r
+Turn on round-robin reading.
+.It Fl R
+Turn off round-robin reading.
 .El
 .It Cm rebuild
 Rebuild the given component forcibly.
@@ -167,10 +177,10 @@ Additional options include:
 Be more verbose.
 .El
 .Sh EXAMPLES
-Use 3 disks to setup a RAID3 array. Create a file system, mount it, then unmount
-it and stop device:
+Use 3 disks to setup a RAID3 array (use round-robin reading feature).
+Create a file system, mount it, then unmount it and stop device:
 .Bd -literal -offset indent
-graid3 label -v data da0 da1 da2
+graid3 label -v -r data da0 da1 da2
 newfs /dev/raid3/data
 mount /dev/raid3/data /mnt
 [...]