netdev - Re: [PATCH net-next v2 13/14] ixgbe: preserve RSS indirection table across admin down/up

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Message-ID: <20251021161006.47e42133@kernel.org>
Date: Tue, 21 Oct 2025 16:10:06 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Kohei Enju <enjuk@...zon.com>
Cc: <aleksander.lobakin@...el.com>, <andrew+netdev@...n.ch>,
 <anthony.l.nguyen@...el.com>, <corbet@....net>, <davem@...emloft.net>,
 <edumazet@...gle.com>, <horms@...nel.org>, <jacob.e.keller@...el.com>,
 <jiri@...nulli.us>, <linux-doc@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
 <pabeni@...hat.com>, <przemyslaw.kitszel@...el.com>, <sx.rinitha@...el.com>
Subject: Re: [PATCH net-next v2 13/14] ixgbe: preserve RSS indirection table
 across admin down/up

On Tue, 21 Oct 2025 12:59:34 +0900 Kohei Enju wrote:
> For example, consider a scenario where the queue count is 8 with user
> configuration containing values from 0 to 7. When queue count changes
> from 8 to 4 and we skip the reinitialization in this scenario, entries
> pointing to queues 4-7 become invalid. The same issue applies when the
> RETA table size changes.

Core should reject this. See ethtool_check_max_channel()

> Furthermore, IIUC, adding netif_is_rxfh_configured() to the current
> condition wouldn't provide additional benefit. When parameters remain
> unchanged, regardless of netif_is_rxfh_configured(), we already preserve
> the RETA entries which might be user-configured or default values, 

User may decide to "isolate" (take out of RSS) a lower queue,
to configure it for AF_XDP or other form of zero-copy. Install
explicit rules to direct traffic to that queue. If you reset
the RSS table random traffic will get stranded in the ZC queue
(== dropped).