Author: sbruno
Date: Sat Apr 27 08:40:37 2013
New Revision: 249977
URL: http://svnweb.freebsd.org/changeset/base/249977
Log:
Change maxio to reflect variable hardware configurations.
If max_sg_length is 0, then we default to 16
If max_sg_length is less than CISS_MAX_SG_ELEMENTS, then
we will set round the value of max_sg_length to the nearest
power of 2 and use it to align maxio.
Else, we will use CISS_MAX_SG_ELEMENTS for our calculations.
Thanks to scottl for working me through the history and providing
the basis for this patch.
Submitted by: scott
Obtained from: Yahoo! Inc.
MFC after: 2 weeks
Modified:
head/sys/dev/ciss/ciss.c
Modified: head/sys/dev/ciss/ciss.c
==============================================================================
--- head/sys/dev/ciss/ciss.c Sat Apr 27 08:11:48 2013 (r249976)
+++ head/sys/dev/ciss/ciss.c Sat Apr 27 08:40:37 2013 (r249977)
@@ -2985,6 +2985,7 @@ ciss_cam_action(struct cam_sim *sim, uni
case XPT_PATH_INQ:
{
struct ccb_pathinq *cpi = &ccb->cpi;
+ int sg_length;
debug(1, "XPT_PATH_INQ %d:%d:%d", cam_sim_bus(sim),
ccb->ccb_h.target_id, ccb->ccb_h.target_lun);
@@ -3005,7 +3006,22 @@ ciss_cam_action(struct cam_sim *sim, uni
cpi->transport_version = 2;
cpi->protocol = PROTO_SCSI;
cpi->protocol_version = SCSI_REV_2;
- cpi->maxio = (min(CISS_MAX_SG_ELEMENTS - 1,
sc->ciss_cfg->max_sg_length)) * PAGE_SIZE;
+ if (sc->ciss_cfg->max_sg_length == 0) {
+ sg_length = 16;
+ } else {
+ /* XXX Fix for ZMR cards that advertise max_sg_length == 32
+ * Confusing bit here. max_sg_length is usually a power of 2. We always
+ * need to subtract 1 to account for partial pages. Then we need to
+ * align on a valid PAGE_SIZE so we round down to the nearest power of
2.
+ * Add 1 so we can then subtract it out in the assignment to maxio.
+ * The reason for all these shenanigans is to create a maxio value that
+ * creates IO operations to volumes that yield consistent operations
+ * with good performance.
+ */
+ sg_length = sc->ciss_cfg->max_sg_length - 1;
+ sg_length = (1 << (fls(sg_length) - 1)) + 1;
+ }
+ cpi->maxio = (min(CISS_MAX_SG_ELEMENTS, sg_length) - 1) * PAGE_SIZE;
ccb->ccb_h.status = CAM_REQ_CMP;
break;
}
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