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

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Date:   Fri, 4 Nov 2022 11:39:32 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Nick Child <nnac123@...ux.ibm.com>
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 Fri, 4 Nov 2022 13:15:39 -0500 Nick Child wrote:
> > Or is the concern coming from your recent work on BQL and having many
> > queues exacerbating buffer bloat?  
> 
> Yes, and Dave can jump in here if I am wrong, but, from my 
> understanding, if the NIC cannot send packets at the rate that
> they are queued then these queues will inevitably fill to txqueuelen.
> In this case, having more queues will not mean better throughput but
> will result in a large number of allocations sitting in queues 
> (bufferbloat). I believe Dave's point was, if more queues does not
> allow for better performance (and can risk bufferbloat) then why
> have so many at all.
> 
> After going through testing and seeing no difference in performance
> with 8 vs 16 queues, I would rather not have the driver be a culprit
> of potential resource hogging.

Right, so my point was that user can always shoot themselves in the
foot with bad configs. You can leave the MAX at 16, in case someone
needs it. Limit the default real queues setting instead, most users
will use the default.