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IB/srp: Reduce number of BUSY conditions

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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_NORMAL_REQ_SQ_SIZE by reducing the
number of BUSY responses reported by ib_srp to the SCSI mid-layer.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
This commit is contained in:
Bart Van Assche 2010-08-30 19:27:36 +00:00 committed by Roland Dreier
parent 05a1d7504f
commit 7ade400aba
1 changed files with 7 additions and 2 deletions
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9
drivers/infiniband/ulp/srp/ib_srp.c
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@ -1339,8 +1339,13 @@ 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);
/*
* Reserve credits for task management so we don't
* bounce requests back to the SCSI mid-layer.
*/
target->scsi_host->can_queue
= min(target->req_lim - SRP_TSK_MGMT_SQ_SIZE,
target->scsi_host->can_queue);
} else {
shost_printk(KERN_WARNING, target->scsi_host,
PFX "Unhandled RSP opcode %#x\n", opcode);