linux-kernel - [PATCH 5/5] virtio: blk/scsi: use block layer helpers to calculate num of queues

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Message-Id: <20250617-isolcpus-queue-counters-v1-5-13923686b54b@kernel.org>
Date: Tue, 17 Jun 2025 15:43:27 +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 5/5] virtio: blk/scsi: 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>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
Reviewed-by: Hannes Reinecke <hare@...e.de>
Reviewed-by: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Daniel Wagner <wagi@...nel.org>
---
 drivers/block/virtio_blk.c | 5 ++---
 drivers/scsi/virtio_scsi.c | 1 +
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 30bca8cb7106040d3bbb11ba9e0b546510534324..e649fa67bac16b4f0c6e8e8f0e6bec111897c355 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -976,9 +976,8 @@ static int init_vq(struct virtio_blk *vblk)
 		return -EINVAL;
 	}

-	num_vqs = min_t(unsigned int,
-			min_not_zero(num_request_queues, nr_cpu_ids),
-			num_vqs);
+	num_vqs = blk_mq_num_possible_queues(
+			min_not_zero(num_request_queues, num_vqs));

 	num_poll_vqs = min_t(unsigned int, poll_queues, num_vqs - 1);

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 21ce3e9401929cd273fde08b0944e8b47e1e66cc..96a69edddbe5555574fc8fed1ba7c82a99df4472 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -919,6 +919,7 @@ static int virtscsi_probe(struct virtio_device *vdev)
 	/* We need to know how many queues before we allocate. */
 	num_queues = virtscsi_config_get(vdev, num_queues) ? : 1;
 	num_queues = min_t(unsigned int, nr_cpu_ids, num_queues);
+	num_queues = blk_mq_num_possible_queues(num_queues);

 	num_targets = virtscsi_config_get(vdev, max_target) + 1;

-- 
2.49.0