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Change maxio to reflect variable hardware configurations.

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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
This commit is contained in:
Sean Bruno 2013-04-27 08:40:37 +00:00
parent c46db3529c
commit bdde570562
1 changed files with 17 additions and 1 deletions
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18
sys/dev/ciss/ciss.c
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@ -2985,6 +2985,7 @@ ciss_cam_action(struct cam_sim *sim, union ccb *ccb)
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, union ccb *ccb)
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;
}