Re: [PATCH V3] NVMe: basic conversion to blk-mq

[Jens Axboe]

On 05/29/2014 05:06 PM, Jens Axboe wrote:
> Ah I see, yes that code apparently got axed. The attached patch brings
> it back. Totally untested, I'll try and synthetically hit it to ensure
> that it does work. Note that it currently does unmap and iod free, so
> the request comes back pristine. We could preserve that if we really
> wanted to, I'm guessing it's not a big deal.

And another totally untested patch that retains the iod and dma mapping
on the requeue event. Again, probably not a big deal, I'm assuming these
happen rarely, but it's simple enough to do.

-- 
Jens Axboe

diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
index 22d8013cd4ff..fd3f11d837bb 100644
--- a/drivers/block/nvme-core.c
+++ b/drivers/block/nvme-core.c
@@ -357,17 +357,22 @@ static void req_completion(struct nvme_queue *nvmeq, void *ctx,
 
 	u16 status = le16_to_cpup(&cqe->status) >> 1;
 
+	if (unlikely(status)) {
+		if (!(status & NVME_SC_DNR || blk_noretry_request(req))
+		    && (jiffies - req->start_time) < req->timeout) {
+			blk_mq_requeue_request(req);
+			return;
+		}
+		req->errors = -EIO;
+	} else
+		req->errors = 0;
+
 	if (iod->nents) {
 		dma_unmap_sg(&nvmeq->dev->pci_dev->dev, iod->sg, iod->nents,
 			rq_data_dir(req) ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
 	}
 	nvme_free_iod(nvmeq->dev, iod);
 
-	if (unlikely(status))
-		req->errors = -EIO;
-	else
-		req->errors = 0;
-
 	blk_mq_complete_request(req);
 }
 
@@ -569,11 +574,19 @@ static int nvme_submit_req_queue(struct nvme_queue *nvmeq, struct nvme_ns *ns,
 	enum dma_data_direction dma_dir;
 	int psegs = req->nr_phys_segments;
 
+	/*
+	 * Requeued IO has already been prepped
+	 */
+	iod = req->special;
+	if (iod)
+		goto submit_iod;
+
 	iod = nvme_alloc_iod(psegs, blk_rq_bytes(req), GFP_ATOMIC);
 	if (!iod)
 		return BLK_MQ_RQ_QUEUE_BUSY;
 
 	iod->private = req;
+	req->special = iod;
 
 	nvme_set_info(cmd, iod, req_completion);
 
@@ -602,6 +615,7 @@ static int nvme_submit_req_queue(struct nvme_queue *nvmeq, struct nvme_ns *ns,
 			goto finish_cmd;
 	}
 
+ submit_iod:
 	if (!nvme_submit_iod(nvmeq, iod, ns))
 		return 0;