RE: [PATCH 1/2] vdpa: Allow to configure max data virtqueues

From: Eli Cohen <redacted>
Sent: Wednesday, December 1, 2021 5:29 PM

On Wed, Dec 01, 2021 at 12:09:17PM +0200, Parav Pandit wrote:

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From: Eli Cohen <redacted>
Sent: Wednesday, December 1, 2021 3:33 PM

On Tue, Nov 30, 2021 at 05:24:03PM -0800, Si-Wei Liu wrote:

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On 11/30/2021 1:48 AM, Eli Cohen wrote:

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Allow to configure the max virtqueues for a device.

Signed-off-by: Eli Cohen <redacted>
---
  drivers/vdpa/vdpa.c  | 16 +++++++++++++++-
  include/linux/vdpa.h |  1 +
  2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index

7332a74a4b00..e185ec2ee851 100644

--- a/drivers/vdpa/vdpa.c
+++ b/drivers/vdpa/vdpa.c

@@ -480,7 +480,8 @@ vdpa_nl_cmd_mgmtdev_get_dumpit(struct

sk_buff

*msg, struct netlink_callback *cb)

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  }
  #define VDPA_DEV_NET_ATTRS_MASK ((1 <<

VDPA_ATTR_DEV_NET_CFG_MACADDR) | \

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-				 (1 <<

VDPA_ATTR_DEV_NET_CFG_MTU))

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+				 (1 <<

VDPA_ATTR_DEV_NET_CFG_MTU) | \

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+				 (1 <<

VDPA_ATTR_DEV_NET_CFG_MAX_VQP))

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It seems VDPA_ATTR_DEV_MAX_VQS (u32) is what you want (# of data
virtqueues instead of # of data virtqueue pairs)? Not sure what's
possible use of VDPA_ATTR_DEV_NET_CFG_MAX_VQP, was it to

dump/display

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the config space max_virtqueue_pairs value (u16, 1-32768) for
virtio-net? Why there's such quasi-duplicate attribute introduced
in the first

place?

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VDPA_ATTR_DEV_MAX_VQS currently returns vdev->nvqs which equals
whatever passed to _vdpa_register_device(). The latter depends on
the value provided by (struct vdpa_dev_set_config).max_virtqueues.

But currently VDPA_ATTR_DEV_MAX_VQS returns the number of used queues,

No. it doesn't.
It reports nvqs passed in _vdpa_register_device().
And this API has clear definition of nvqs = number of virtqueues supported by this device
nvqs != number of used vqs.
So current MAX_VQS is doing its job right.
For example nvqs can be be 8 and guest VM driver may just use two VQs (1 tx, 1 rx, and used vqs = 2).
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