linux-kernel - [PATCH] nvme: Acknowledge completion queue on each iteration

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Date:   Mon, 17 Jul 2017 18:36:23 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-nvme@...ts.infradead.org, timur@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>, linux-kernel@...r.kernel.org
Subject: [PATCH] nvme: Acknowledge completion queue on each iteration

Code is moving the completion queue doorbell after processing all completed
events and sending callbacks to the block layer on each iteration.

This is causing a performance drop when a lot of jobs are queued towards
the HW. Move the completion queue doorbell on each loop instead and allow new
jobs to be queued by the HW.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/nvme/host/pci.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index d10d2f2..33d9b5b 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -810,13 +810,12 @@ static void nvme_process_cq(struct nvme_queue *nvmeq)
 
 	while (nvme_read_cqe(nvmeq, &cqe)) {
 		nvme_handle_cqe(nvmeq, &cqe);
+		nvme_ring_cq_doorbell(nvmeq);
 		consumed++;
 	}
 
-	if (consumed) {
-		nvme_ring_cq_doorbell(nvmeq);
+	if (consumed)
 		nvmeq->cqe_seen = 1;
-	}
 }
 
 static irqreturn_t nvme_irq(int irq, void *data)
-- 
1.9.1