linux-kernel - [PATCH 2/2] nvme-pci: don't allocate unused I/O queues

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Date:   Thu, 12 Nov 2020 09:23:02 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     linux-nvme@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, Keith Busch <kbusch@...nel.org>,
        Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: [PATCH 2/2] nvme-pci: don't allocate unused I/O queues

currently the NVME_QUIRK_SHARED_TAGS quirk for Apple devices is handled
during the assignment of nr_io_queues in nvme_setup_io_queues().
This however means that for these devices nvme_max_io_queues() will
actually not return the supported maximum which is confusing and
unexpected and also means that in nvme_probe() we are allocating
for I/O queues that will never be used.
Fix this by moving the quirk handling into nvme_max_io_queues().

Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
---
 drivers/nvme/host/pci.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index b56250b83bdf..0f8cea5b30eb 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2089,6 +2089,12 @@ static void nvme_disable_io_queues(struct nvme_dev *dev)
 
 static unsigned int nvme_max_io_queues(struct nvme_dev *dev)
 {
+	/*
+	 * If tags are shared with admin queue (Apple bug), then
+	 * make sure we only use one IO queue.
+	 */
+	if (dev->ctrl.quirks & NVME_QUIRK_SHARED_TAGS)
+		return 1;
 	return num_possible_cpus() + dev->nr_write_queues + dev->nr_poll_queues;
 }
 
@@ -2107,15 +2113,7 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
 	dev->nr_write_queues = write_queues;
 	dev->nr_poll_queues = poll_queues;
 
-	/*
-	 * If tags are shared with admin queue (Apple bug), then
-	 * make sure we only use one IO queue.
-	 */
-	if (dev->ctrl.quirks & NVME_QUIRK_SHARED_TAGS)
-		nr_io_queues = 1;
-	else
-		nr_io_queues = dev->nr_allocated_queues - 1;
-
+	nr_io_queues = dev->nr_allocated_queues - 1;
 	result = nvme_set_queue_count(&dev->ctrl, &nr_io_queues);
 	if (result < 0)
 		return result;
-- 
2.17.1