nvmet: handle rw's limited retry flag

In some scenarios, some multipath software setup places the
REQ_FAILFAST_DEV flag on I/O to prevent retries and immediately
switch to other paths for issuing I/O commands. This will reflect
on the NVMe read and write commands with the limited retry flag.

However, the current NVMe target side does not handle the limited
retry flag, and the target's underlying driver still retries the
I/O. This will result in the I/O not being quickly switched to
other paths, ultimately leading to increased I/O latency.

When the nvme target receive an rw command with limited retry flag,
handle it in block backend by setting the REQ_FAILFAST_DEV flag to
bio.

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>

diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
index 0bda83d..6380b60 100644 (file)
--- a/drivers/nvme/target/io-cmd-bdev.c
+++ b/drivers/nvme/target/io-cmd-bdev.c
@@ -272,6 +272,9 @@ static void nvmet_bdev_execute_rw(struct nvmet_req *req)
                iter_flags = SG_MITER_FROM_SG;
        }
 
+       if (req->cmd->rw.control & NVME_RW_LR)
+               opf |= REQ_FAILFAST_DEV;
+
        if (is_pci_p2pdma_page(sg_page(req->sg)))
                opf |= REQ_NOMERGE;