netdev - Re: [PATCH v2 net] ibmveth: Reduce maximum tx queues to 8

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Message-ID: <4f84f10b-9a79-17f6-7e2e-f65f0d2934cb@linux.ibm.com>
Date:   Fri, 4 Nov 2022 09:06:02 -0500
From:   Nick Child <nnac123@...ux.ibm.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, nick.child@....com, bjking1@...ux.ibm.com,
        ricklind@...ibm.com, dave.taht@...il.com
Subject: Re: [PATCH v2 net] ibmveth: Reduce maximum tx queues to 8



On 11/3/22 22:59, Jakub Kicinski wrote:
> On Wed,  2 Nov 2022 13:38:37 -0500 Nick Child wrote:
>> Previously, the maximum number of transmit queues allowed was 16. Due to
>> resource concerns, limit to 8 queues instead.
>>
>> Since the driver is virtualized away from the physical NIC, the purpose
>> of multiple queues is purely to allow for parallel calls to the
>> hypervisor. Therefore, there is no noticeable effect on performance by
>> reducing queue count to 8.
> 
> I'm not sure if that's the point Dave was making but we should be
> influencing the default, not the MAX. Why limit the MAX?

The MAX is always allocated in the drivers probe function. In the 
drivers open and ethtool-set-channels functions we set 
real_num_tx_queues. So the number of allocated queues is always MAX
but the number of queues actually in use may differ and can be set by 
the user.
I hope this explains. Otherwise, please let me know.

Thanks again for taking the time to review,
Nick Child