linux-kernel - [PATCH 3/5] nvme-pci: use block layer helpers to calculate num of queues

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Message-Id: <20250617-isolcpus-queue-counters-v1-3-13923686b54b@kernel.org>
Date: Tue, 17 Jun 2025 15:43:25 +0200
From: Daniel Wagner <wagi@...nel.org>
To: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>
Cc: Keith Busch <kbusch@...nel.org>, Sagi Grimberg <sagi@...mberg.me>, 
 "Michael S. Tsirkin" <mst@...hat.com>, 
 "Martin K. Petersen" <martin.petersen@...cle.com>, 
 Thomas Gleixner <tglx@...utronix.de>, 
 Costa Shulyupin <costa.shul@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, 
 Valentin Schneider <vschneid@...hat.com>, Waiman Long <llong@...hat.com>, 
 Ming Lei <ming.lei@...hat.com>, Frederic Weisbecker <frederic@...nel.org>, 
 Hannes Reinecke <hare@...e.de>, linux-kernel@...r.kernel.org, 
 linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org, 
 megaraidlinux.pdl@...adcom.com, linux-scsi@...r.kernel.org, 
 storagedev@...rochip.com, virtualization@...ts.linux.dev, 
 GR-QLogic-Storage-Upstream@...vell.com, Daniel Wagner <wagi@...nel.org>
Subject: [PATCH 3/5] nvme-pci: use block layer helpers to calculate num of
 queues

The calculation of the upper limit for queues does not depend solely on
the number of possible CPUs; for example, the isolcpus kernel
command-line option must also be considered.

To account for this, the block layer provides a helper function to
retrieve the maximum number of queues. Use it to set an appropriate
upper queue number limit.

Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Hannes Reinecke <hare@...e.de>
Signed-off-by: Daniel Wagner <wagi@...nel.org>
---
 drivers/nvme/host/pci.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 8ff12e415cb5d1529d760b33f3e0cf3b8d1555f1..f134bf4f41b2581e4809e618250de7985b5c9701 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -97,7 +97,7 @@ static int io_queue_count_set(const char *val, const struct kernel_param *kp)
 	int ret;

 	ret = kstrtouint(val, 10, &n);
-	if (ret != 0 || n > num_possible_cpus())
+	if (ret != 0 || n > blk_mq_num_possible_queues(0))
 		return -EINVAL;
 	return param_set_uint(val, kp);
 }
@@ -2520,7 +2520,8 @@ static unsigned int nvme_max_io_queues(struct nvme_dev *dev)
 	 */
 	if (dev->ctrl.quirks & NVME_QUIRK_SHARED_TAGS)
 		return 1;
-	return num_possible_cpus() + dev->nr_write_queues + dev->nr_poll_queues;
+	return blk_mq_num_possible_queues(0) + dev->nr_write_queues +
+		dev->nr_poll_queues;
 }

 static int nvme_setup_io_queues(struct nvme_dev *dev)

-- 
2.49.0