On 7/27/2022 11:47 AM, Parav Pandit wrote:

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From: Zhu, Lingshan <redacted>
Sent: Tuesday, July 26, 2022 10:53 PM

On 7/27/2022 10:17 AM, Parav Pandit wrote:

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From: Zhu, Lingshan <redacted>
Sent: Tuesday, July 26, 2022 10:15 PM

On 7/26/2022 11:56 PM, Parav Pandit wrote:

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From: Zhu, Lingshan <redacted>
Sent: Tuesday, July 12, 2022 11:46 PM

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When the user space which invokes netlink commands, detects that

_MQ

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is not supported, hence it takes max_queue_pair = 1 by itself.
I think the kernel module have all necessary information and it is
the only one which have precise information of a device, so it
should answer precisely than let the user space guess. The kernel
module should be reliable than stay silent, leave the question to
the user space

tool.

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Kernel is reliable. It doesn’t expose a config space field if the
field doesn’t

exist regardless of field should have default or no default.
so when you know it is one queue pair, you should answer one, not try
to guess.

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User space should not guess either. User space gets to see if _MQ

present/not present. If _MQ present than get reliable data from kernel.

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If _MQ not present, it means this device has one VQ pair.

it is still a guess, right? And all user space tools implemented this
feature need to guess

No. it is not a guess.
It is explicitly checking the _MQ feature and deriving the value.
The code you proposed will be present in the user space.
It will be uniform for _MQ and 10 other features that are present now and

in the future.
MQ and other features like RSS are different. If there is no _RSS_XX, there
are no attributes like max_rss_key_size, and there is not a default value.
But for MQ, we know it has to be 1 wihtout _MQ.

"we" = user space.
To keep the consistency among all the config space fields.

The user space tools asks for the number of vq pairs, not whether the 
device has _MQ.
_MQ and _RSS are not the same kind of concepts, as we have discussed above.
You have pointed out the logic: If there is _MQ, kernel answers 
max_vq_paris, if no _MQ, num_vq_paris=1.

So as MST pointed out, implementing this in kernel space can make our 
life easier, once for all.

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For feature X, kernel reports default and for feature Y, kernel skip

reporting it, because there is no default. <- This is what we are trying to
avoid here.
Kernel reports one queue pair because there is actually one.