When doing round-robin reads from a multi-plex volume, only switch to the

next plex if the sector to be read isn't nearby the last read sector.

Submitted by:  Vsevolod Lobko <seva@ip.net.ua> via ru@
Approved by:   grog (mentor)

3 files changed, 20 insertions, 4 deletions

diff --git a/sys/dev/vinum/vinumobj.h b/sys/dev/vinum/vinumobj.h
index 81087f3..0d5b800 100644
--- a/sys/dev/vinum/vinumobj.h
+++ b/sys/dev/vinum/vinumobj.h
@@ -275,6 +275,7 @@ struct _plex
 #ifdef _KERNEL
     struct rangelock *lock;				    /* ranges of locked addresses */
     struct mtx *lockmtx;				    /* lock mutex, one of plexmutex [] */
+    daddr_t last_addr;					    /* last address read from this plex */
     dev_t dev;						    /* associated device */
 #endif
 };
diff --git a/sys/dev/vinum/vinumrequest.c b/sys/dev/vinum/vinumrequest.c
index eda4c2a..0915f8c 100644
--- a/sys/dev/vinum/vinumrequest.c
+++ b/sys/dev/vinum/vinumrequest.c
@@ -234,10 +234,18 @@ vinumstart(struct buf *bp, int reviveok)
 	if (vol != NULL) {
 	    plexno = vol->preferred_plex;		    /* get the plex to use */
 	    if (plexno < 0) {				    /* round robin */
-		plexno = vol->last_plex_read;
-		vol->last_plex_read++;
-		if (vol->last_plex_read >= vol->plexes)	    /* got the the end? */
-		    vol->last_plex_read = 0;		    /* wrap around */
+		for (plexno = 0; plexno < vol->plexes; plexno++)
+		    if (abs(bp->b_blkno - PLEX[vol->plex[plexno]].last_addr) <= ROUNDROBIN_SWITCH)
+		        break;
+		if (plexno >= vol->plexes) {
+		    vol->last_plex_read++;
+		    if (vol->last_plex_read >= vol->plexes)
+			vol->last_plex_read = 0;
+		    plexno = vol->last_plex_read;
+		} else {
+		    vol->last_plex_read = plexno;
+		};
+		PLEX[vol->plex[plexno]].last_addr = bp->b_blkno;
 	    }
 	    status = build_read_request(rq, plexno);	    /* build a request */
 	} else {
diff --git a/sys/dev/vinum/vinumvar.h b/sys/dev/vinum/vinumvar.h
index 807439c..8e7edd8 100644
--- a/sys/dev/vinum/vinumvar.h
+++ b/sys/dev/vinum/vinumvar.h
@@ -361,6 +361,13 @@ enum parityop {
     rebuildandcheckparity,				    /* rebuildparity with the -v option */
 };
 
+/*
+ * When doing round-robin reads from a multi-plex volume, switch to the
+ * next plex if the difference of the last read sector and the next sector
+ * to be read is this many sectors.
+ */
+#define ROUNDROBIN_SWITCH	128			    /* 64k */
+
 #ifdef VINUMDEBUG
 /* Debugging stuff */
 enum debugflags {