linux-kernel - [PATCH 3.18 183/185] scsi: lpfc: Fix frequency of Release WQE CQEs

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Date:   Mon, 28 May 2018 12:03:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dick Kennedy <dick.kennedy@...adcom.com>,
        James Smart <james.smart@...adcom.com>,
        Hannes Reinecke <hare@...e.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 3.18 183/185] scsi: lpfc: Fix frequency of Release WQE CQEs

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: James Smart <jsmart2021@...il.com>

[ Upstream commit 04673e38f56b30cd39b1fa0f386137d818b17781 ]

The driver controls when the hardware sends completions that communicate
consumption of elements from the WQ. This is done by setting a WQEC bit
on a WQE.

The current driver sets it on every Nth WQE posting. However, the driver
isn't clearing the bit if the WQE is reused. Thus, if the queue depth
isn't evenly divisible by N, with enough time, it can be set on every
element, creating a lot of overhead and risking CQ full conditions.

Correct by clearing the bit when not setting it on an Nth element.

Signed-off-by: Dick Kennedy <dick.kennedy@...adcom.com>
Signed-off-by: James Smart <james.smart@...adcom.com>
Reviewed-by: Hannes Reinecke <hare@...e.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/scsi/lpfc/lpfc_sli.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/scsi/lpfc/lpfc_sli.c
+++ b/drivers/scsi/lpfc/lpfc_sli.c
@@ -115,6 +115,8 @@ lpfc_sli4_wq_put(struct lpfc_queue *q, u
 	/* set consumption flag every once in a while */
 	if (!((q->host_index + 1) % q->entry_repost))
 		bf_set(wqe_wqec, &wqe->generic.wqe_com, 1);
+	else
+		bf_set(wqe_wqec, &wqe->generic.wqe_com, 0);
 	if (q->phba->sli3_options & LPFC_SLI4_PHWQ_ENABLED)
 		bf_set(wqe_wqid, &wqe->generic.wqe_com, q->queue_id);
 	lpfc_sli_pcimem_bcopy(wqe, temp_wqe, q->entry_size);