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

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Message-ID: <20251021040000.15434-1-enjuk@amazon.com>
Date: Tue, 21 Oct 2025 12:59:34 +0900
From: Kohei Enju <enjuk@...zon.com>
To: <kuba@...nel.org>
CC: <aleksander.lobakin@...el.com>, <andrew+netdev@...n.ch>,
	<anthony.l.nguyen@...el.com>, <corbet@....net>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <enjuk@...zon.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 Mon, 20 Oct 2025 18:32:46 -0700, Jakub Kicinski wrote:

>On Thu, 16 Oct 2025 23:08:42 -0700 Jacob Keller wrote:
>> Currently, the RSS indirection table configured by user via ethtool is
>> reinitialized to default values during interface resets (e.g., admin
>> down/up, MTU change). As for RSS hash key, commit 3dfbfc7ebb95 ("ixgbe:
>> Check for RSS key before setting value") made it persistent across
>> interface resets.
>> 
>> Adopt the same approach used in igc and igb drivers which reinitializes
>> the RSS indirection table only when the queue count changes. Since the
>> number of RETA entries can also change in ixgbe, let's make user
>> configuration persistent as long as both queue count and the number of
>> RETA entries remain unchanged.
>
>We should take this a step further and also not reinitialize if 
>netif_is_rxfh_configured(). Or am I missing something?

Hi Jakub, thank you for reviewing.

Actually, you raise a good point about netif_is_rxfh_configured().

However, we can't determine whether we should reinitialize or not based
solely on netif_is_rxfh_configured(), since the RETA table is determined
by (1) the queue count and (2) the size of RETA table.

So, simply skipping reinitialization on netif_is_rxfh_configured() would
leave invalid RETA entries when those parameters are to be changed.

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.

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, 

Therefore I believe the current logic is correct as is, and we should
reinitialize the RETA entries when either parameter changes, regardless
of netif_is_rxfh_configured().