New drives have much more sophisticated IO queueing algorithms and
posses much more information about the physical limitations of drive
platters (or lack thereof) than an OS can ever hope to have. So switch
SCSI (and SATA) drives to use the shiny new bufq that does not sort IOs.
Essentially this keeps IOs closer to the drive.
The impact I have seen is negligible noise in sequential IO however
random IO seems to get a 20 - 25 % performance benefit.
I'd like to commit this soon so speak now or forever hold your piece.
Index: sd.c
===================================================================
RCS file: /cvs/src/sys/scsi/sd.c,v
retrieving revision 1.198
diff -u -p -r1.198 sd.c
--- sd.c 28 Jun 2010 08:35:46 -0000 1.198
+++ sd.c 30 Jun 2010 18:38:20 -0000
@@ -182,7 +182,11 @@ sdattach(struct device *parent, struct d
*/
sc->sc_dk.dk_driver = &sddkdriver;
sc->sc_dk.dk_name = sc->sc_dev.dv_xname;
- sc->sc_bufq = bufq_init(BUFQ_DEFAULT);
+
+ if (SCSISPC(sc_link->inqdata.version) >= 2)
+ sc->sc_bufq = bufq_init(BUFQ_FIFO);
+ else
+ sc->sc_bufq = bufq_init(BUFQ_DEFAULT);
if ((sc_link->flags & SDEV_ATAPI) && (sc_link->flags & SDEV_REMOVABLE))
sc_link->quirks |= SDEV_NOSYNCCACHE;
