As proposed by the SRP (draft) standard, ib_srp reserves one ring element for
SRP_TSK_MGMT requests. This patch makes sure that the SCSI mid-layer never
tries to queue more than (SRP request limit) - 1 SCSI commands to ib_srp. This
improves performance for targets whose request limit is less than or equal to
SRP_SQ_REQ_SIZE - SRP_TSK_MGMT_RSV (62) by reducing the number of BUSY
responses reported by ib_srp to the SCSI mid-layer.
Signed-off-by: Bart Van Assche <bvanass...@acm.org>
Cc: Roland Dreier <rola...@cisco.com>
Cc: David Dillow <d...@thedillows.org>
---
drivers/infiniband/ulp/srp/ib_srp.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/infiniband/ulp/srp/ib_srp.c
b/drivers/infiniband/ulp/srp/ib_srp.c
index cc6a713..93d6d0f 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -1354,8 +1354,13 @@ static int srp_cm_handler(struct ib_cm_id *cm_id, struct
ib_cm_event *event)
target->max_ti_iu_len = be32_to_cpu(rsp->max_ti_iu_len);
target->req_lim = be32_to_cpu(rsp->req_lim_delta);
- target->scsi_host->can_queue = min(target->req_lim,
-
target->scsi_host->can_queue);
+ /*
+ * Set can_queue such that the SCSI mid-layer
+ * never causes __srp_get_tx_iu() to fail.
+ */
+ target->scsi_host->can_queue
+ = min(target->req_lim - SRP_TSK_MGMT_RSV,
+ target->scsi_host->can_queue);
} else {
shost_printk(KERN_WARNING, target->scsi_host,
PFX "Unhandled RSP opcode %#x\n", opcode);
--
1.6.4.2
--
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