netdev - Re: [RFC net-next v3 2/4] virtio_net: Prepare for NAPI to queue mapping

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Message-ID: <20250127133304.7898e4c2@kernel.org>
Date: Mon, 27 Jan 2025 13:33:04 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Joe Damato <jdamato@...tly.com>
Cc: Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
 gerhard@...leder-embedded.com, leiyang@...hat.com,
 xuanzhuo@...ux.alibaba.com, mkarsten@...terloo.ca, "Michael S. Tsirkin"
 <mst@...hat.com>, Eugenio Pérez <eperezma@...hat.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, "open list:VIRTIO CORE AND NET DRIVERS"
 <virtualization@...ts.linux.dev>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next v3 2/4] virtio_net: Prepare for NAPI to queue
 mapping

On Mon, 27 Jan 2025 14:31:21 -0500 Joe Damato wrote:
> Actually, I missed a patch Jakub submit to net [1], which prevents
> dumping TX-only NAPIs.

That patch only addresses NAPI ops, here I think we're talking about
attributes of the queue object.

> So, I think this RFC as-is (only calling netif_queue_set_napi
> for RX NAPIs) should be fine without changes.

Weak preference towards making netdev_nl_queue_fill_one() "do the right
thing" when NAPI does not have ID assigned. And right thing IMO would
be to skip reporting the NAPI_ID attribute.

Tx NAPIs are one aspect, whether they have ID or not we may want direct
access to the struct somewhere in the core, via txq, at some point, and
then people may forget the linking has an unintended effect of also
changing the netlink attrs. The other aspect is that driver may link
queue to a Rx NAPI instance before napi_enable(), so before ID is
assigned. Again, we don't want to report ID of 0 in that case.