On Wed, 22 Oct 2025 12:40:45 +0900 Kohei Enju wrote:

On Tue, 21 Oct 2025 16:10:06 -0700, Jakub Kicinski wrote:

quoted

On Tue, 21 Oct 2025 12:59:34 +0900 Kohei Enju wrote:  

quoted

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()  

Indeed, you're right that the situation above will be rejected. I missed
it.

BTW, I think reinitializing the RETA table when queue count changes or
RETA table size changes is reasonable for predictability and safety.
Does this approach make sense to you?

Yes, if !netif_is_rxfh_configured() re-initializing is expected.

quoted

quoted

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).

You're correct about the ZC queue scenario. The original implementation
(before this patch) would indeed cause this problem by unconditionally
reinitializing.

I believe this patch addresses that issue - it preserves the user
configuration since neither queue count nor RETA table size changes in
that case. If I'm misunderstanding your scenario, please let me know.

I could update the logic to explicitly check netif_is_rxfh_configured()
as in [1], though the actual behavior would be the same as [2] since
the default RETA table is a deterministic function of (rss_indices,
reta_entries):

[1] Check user configuration explicitly:
    if (!netif_is_rxfh_configured(adapter->netdev) ||
        adapter->last_rss_indices != rss_i ||
        adapter->last_reta_entries != reta_entries) {
        // reinitialize
    }

[2] Current patch:
    if (adapter->last_rss_indices != rss_i ||
        adapter->last_reta_entries != reta_entries) {
        // reinitialize
    }

Do you have any preference between these approaches, or would you
recommend a different solution?

I was expecting something like:

if (netif_is_rxfh_configured(adapter->netdev)) {
	if (!check_that_rss_is_okay()) {
		/* This should never happen, barring FW errors etc */
		warn("user configuration lost due to XYZ");
		reinit();
	}
} else if (...rss_ind != rss_id ||
           ...reta_entries != reta_entries) {
	reinit();
}