From 58e75cf714fced7ba61602a776441d3d289e8cdc Mon Sep 17 00:00:00 2001
From: John Levon <john.levon@nutanix.com>
Date: Tue, 8 Feb 2022 10:49:43 +0000
Subject: [PATCH] nvmf/vfio-user: avoid division in cq_is_full()

Avoid using the modulus operator in the hot-path cq_is_full(),
by aping how cq_tail_advance() is written.

Signed-off-by: John Levon <john.levon@nutanix.com>
Change-Id: Idbdf1715ab30d08233b38aa7691f0212ae93a542
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/11445
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Community-CI: Mellanox Build Bot
---
 lib/nvmf/vfio_user.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/lib/nvmf/vfio_user.c b/lib/nvmf/vfio_user.c
index 58cd85165..99dec9874 100644
--- a/lib/nvmf/vfio_user.c
+++ b/lib/nvmf/vfio_user.c
@@ -469,6 +469,23 @@ cq_tail_advance(struct nvmf_vfio_user_cq *cq)
 	}
 }
 
+static inline bool
+cq_is_full(struct nvmf_vfio_user_ctrlr *ctrlr, struct nvmf_vfio_user_cq *cq)
+{
+	uint32_t qindex;
+
+	assert(ctrlr != NULL);
+	assert(cq != NULL);
+
+	qindex = *cq_tailp(cq) + 1;
+	if (spdk_unlikely(qindex == cq->size)) {
+		qindex = 0;
+	}
+
+	return qindex == *cq_dbl_headp(ctrlr, cq);
+}
+
+
 /* TODO: wrapper to data structure */
 static inline size_t
 vfio_user_migr_data_len(void)
@@ -978,16 +995,6 @@ asq_setup(struct nvmf_vfio_user_ctrlr *ctrlr)
 	return 0;
 }
 
-static inline bool
-cq_is_full(struct nvmf_vfio_user_ctrlr *ctrlr,
-	   struct nvmf_vfio_user_cq *cq)
-{
-	assert(ctrlr != NULL);
-	assert(cq != NULL);
-
-	return ((*cq_tailp(cq) + 1) % cq->size) == *cq_dbl_headp(ctrlr, cq);
-}
-
 static int
 acq_setup(struct nvmf_vfio_user_ctrlr *ctrlr)
 {